Einstein's theory of relativity faces satellite test

An artist's impression of the French National Centre for Space Studies satellite Microscope, which scientists hope will help fin
An artist's impression of the French National Centre for Space Studies satellite Microscope, which scientists hope will help find a gap in the general relativity theory developed by Albert Einstein
Einstein's theory of general relativity is to be put to the test by a newly launched satellite in an experiment that could upend our understanding of physics.

The French "Microscope" orbiter will try to poke a hole in one of Einstein's most famous theories, which provides the basis for our modern understanding of gravity.

Scientists will use the kit to measure how two different pieces of metal—one titanium and the other a platinum-rhodium alloy—behave in orbit.

"In space, it is possible to study the relative motion of two bodies in almost perfect and permanent free fall aboard an orbiting satellite, shielded from perturbations encountered on Earth," said Arianespace, which put the satellite into orbit on Monday.

Einstein's theory suggests that in perfect free-fall, the two objects should move in exactly the same way. But if they are shown to behave differently "the principle will be violated: an event that would shake the foundations of physics", Arianespace added.

Also aboard the Russian Soyuz rocket launched from French Guiana was an Earth-observation satellite equipped with radar to monitor the planet's surface to track climate and environmental change and help in disaster relief operations.

That satellite, along with another launched two years ago, is part of the 3.8-billion-euro ($4.3-billion) Copernicus project, which will ultimately boast six orbiters in all.

Three previous launches from Arianespace's Spaceport in French Guiana, an overseas territory that borders Brazil, were delayed by poor weather and technical issues.

A countdown on Sunday was halted after scientists observed an "anomaly", the agency said in an earlier statement, while adverse weather conditions had thwarted other attempts.


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Apr 26, 2016
It's flawed.
At the VERY beginning it states:"the relative motion of two bodies in almost perfect and permanent free fall".
For sure the close Earth orbit is NOT a perfect location for a experiment like this.
How in heaven will the algorithim designed to differentiate the behaviours of the two metal plates and the "gravitational anomalies" caused by a constant acceleration satellite?
The satellite is in circular orbit, isn't it? If it behaved as a perfect non-accelerated body it would move in a straight line.
Besides, the Earth is not homogeneous - therefore satellites can map its internal structure while mapping its gravitational field variations - and will affect the two metal plates jamming the signal coming from them in a very tiny way, or not?
How the data will tell which is which?

Apr 26, 2016
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Apr 26, 2016
As someone untrained in this field. I like the experiment.

I expect it will provide some result other than what Einstein predicted. Though I expect the result will be made to awkwardly conform to Einstein's theory in another in a very long line of typically mathematical parlor tricks. Mathematics can be used to provide an explanation for anything we desire. But the Universe is not mathematical. It's nothing of the sort.

Gravity as an explanation does not provide for a Universe that is blowing itself apart, ever faster.

Apr 26, 2016
This comment has been removed by a moderator.

Apr 26, 2016
"That satellite, along with another launched two years ago, is part of the 3.8-billion-euro ($4.3-billion) Copernicus project, which will ultimately boast six orbiters in all."

That is not correct. Copernicus (including services) costs 6.7 Billion euros in total (around 7.5 billion dollars). With 4.3 Billion Euros (not dollars) spend between 2014 and 2020.

The satellites are 12 in total (not 6) with each sentinel mission consisting of 2 satellites each. On top of this some instruments will be placed on other European (weather) satellites separately.

http://europa.eu/...1_en.htm

Apr 26, 2016
The satellite is in circular orbit, isn't it? If it behaved as a perfect non-accelerated body it would move in a straight line.


This test is going to be conducted using Relativistic physics, not Newtonian. In Newtonian physics, a straight line motion not under the action of a net external force would be non-accelerated, but in Relativistic physics, non-accelerated motion follows geodesics instead of straight lines. Orbital free fall is an example of a Space-Time geodesic.

Apr 26, 2016
It's flawed.


Why did you think we would need to read your random, uninformed mumbling?

It's FINE to ask questions, not ok to lead with "It's flawed" and then proceed to demonstrate your ignorance on the matter. Just stop.

Allow me to demonstrate a better question: Can someone help explain the mathematics behind this and the relative-sizes of expected effects such as gravitational variations, dark matter, and how they might isolate or separate out such effects from the data?

BTW you missed about 100 problems, for example changes in magnetic moment on the satellite: http://sci2.esa.i...inal.pdf

There are also dozens of relevant published papers.

Perhaps a better judge of intelligence than "what you know" is the questions you ask when you don't?

Apr 26, 2016
My previous link was working but is now returning 403 -- might be temporary -- link from https://directory...croscope which also has lots of info.

You can still get from cache for now:

http://webcache.g...mp;gl=us

Apr 26, 2016
Can anyone explain in non-technical terms, if relativity say gravity is produced by the bend of space-time by a massive object, then how is space-time measured? And what is the nature of space-time that makes it "bendable"?

Apr 26, 2016
1) Speed of light (in a vacuum) is constant. Always.
2) Light moves in a straight line (for definition of 'straight' look up the term 'geodesic'). Always.

This makes it appear as if light can be bent (e.g. lensing) but it really travels in a straight line. Space is bent.

then how is space-time measured?

To measure something you need a constant ruler. Now, if spacetime is not absolute (cartesian) then something like a metal ruler will not work, because it will potentially stretch/bend/contract with relative motion.
But we have a 'ruler' which all observers moving relative to one another agree on': The speed of light. So that's the thing anything is measured by.

Apr 26, 2016
It's flawed.

You smoked too much pot.
Quite ok for a guru, but incompatible with physics.[/

I kemp screwing. You desert you "5"

Apr 26, 2016
Thanks antialias_physorg. So basically you meassure the lensing of light, is that it? So, aren't you meassuring just the circunference of the massive object that creates the lensing? How can you messure space-time itself? Not just empty space, but the stuff that makes space-time? Unless space-time and empty space is just the same thing, which is what I can inferr from your answer. And what is the nature of space-time that makes it "bendable".

Apr 26, 2016
Space time isn't a stuff. It's not a thing. It's the set of all measurements you can make with rulers and clocks.

The thing is, if you move relative to someone else, you disagree on how long your rulers are, or how fast your clocks tick.

General Relativity just extends this "relative" measurement of lengths and times to also account for the apparent fact that rulers and clocks *also* change depending on how mass and energy and momentum and stuff are distributed. Why is that so? We don't know yet. But we have, in many ways measured it to be a fact. The way you measure length, the way you measure time, it depends on what "stuff" is around you.

Apr 26, 2016
"Only pot can do this"

No. Don't bring pot down to his level please. I understand this perfectly.

Apr 26, 2016
Here is something....speed of light= ds/dt=300,000km/sec.....just restates our measurement system. However, a 'relative system' where space is warped in 3D by gravitational or other forces yet to be discovered like the 'warp field' generated by lasers and EmDrive tuned cavities, will warp the 'measuring sticks' along with the waves to always yield results pleasing to scholasticists. Such will always exult and exclaim: "Teeeee! We are right!" So one needs an observer in true four dimensional hypercartesian space to truly see the true dimensions. That said, projections of the three-D space onto the fourth dimension will have to be corrected with the appropriate trigonometric transformations. This will confuse many people not familiar with higher math.

Apr 27, 2016
@dejesusluisx
Can anyone explain in non-technical terms, if relativity say gravity is produced by the bend of space-time by a massive object, then how is space-time measured?
@antialias' explanation is pretty good. The short answer is you use lasers or point sources like stars. We used laser interferometers to detect the gravity waves you might have heard about recently at the aLIGO observatories. We could see the ripples in spacetime with those lasers.

And what is the nature of space-time that makes it "bendable"?
A very interesting question, with a lot of really complicated answers. There are answers from General Relativity Theory, and there are answers from cosmology (mostly via GRT), and there are answers from quantum mechanics, and there are answers from something called the "Casimir effect," and they're all good answers but they don't always match up with one another (though we're working on that). How much time you got? ;)

BTW good questions. A 5 from me.

Apr 27, 2016
@shavera
Space time isn't a stuff. It's not a thing. It's the set of all measurements you can make with rulers and clocks.
I disagree with this, on several grounds.

First, there's Newton's Bucket. Let's suppose you did a version of Newton's Bucket out between galaxies, which is about as flat as spacetime gets: two rocks and a rope, spinning. Would the rope pull taut? And if it did, they're spinning around each other relative to what, exactly? The minuscule gravity from distant galaxies, that's not even sufficient to pull all the neutral hydrogen out there to them?

Then there's the Casimir Effect. Empty space pushing two plates together. What's pushing? And this demonstrates vacuum energy in the lab.

Then there's the fact that acceleration is absolute; you can always measure if you're accelerating; just drop something. Accelerating relative to what, exactly? Those distant galaxies again?

Spacetime *is* a thing; it's just not a *material* thing.

Apr 27, 2016
The vacuum energy in the Casimir effect should be (has not been verified yet) to be the zero-point energy of the particle fields. [ https://en.wikipe...r_effect ] Same goes for dark energy in cosmology (also not verified).

In other words, these effects should fit Wilzsek's Core Theory (now that the Higgs has completed the Standard Model of particles) or what used to be called the semiclassical approximation (quantum field theory of all particle fields + gravity).

As for spectime of GR, you can speak of strain et cetera in the equations, but I hear [not having studied GR] that if you look carefully the analogy breaks down - spacetime is not a material. Spacetime may curve but it hasn't been 'bent'. Curvature is a good model - in fact used in the equations so a perfectly good model - but as any model it doesn't have to have a deeper meaning. It just is.

Apr 27, 2016
Also, we know that GR - Core Theory spacetime - breaks down in black holes, when gravity (curvature) becomes too strong, because the equations produce a singularity. People use to say that we need a quantum gravity theory then, because nature is quantum mechanical at its core.

However, it doesn't seem like gravity likes to be replaced. You can quantize it and derive gravitons at low energies, meaning it mimics a field already. Photon timing and polarization observations of supernovas predicts that relative distances (relativity!) in spacetime are smooth at all scales, instead of breaking down at Planck scales. If so the question is erroneously answered, and perhaps what is needed is some smooth amalgam of existing fields. There is a seed to such a theory out there, which 'saves' gravity from the so called UV problem. "asymptotically safe gravity'. [ http://www.forbes...70ac3f75 ]

Apr 27, 2016
How can you messure space-time itself?

You can measure spacetime curvature. E.g. the LIGO experiment that discovered gravitational waves is such a measuring device. Also anything where you have to correct for time dialtion (needed for making GPS work) can give you an indication that space is warped. But measuring spacetime 'itself' is tricky. It's not a 'thing'. It's an environment for things to be in. It's geometry - not particle physics. (i realize that this answer won't satisfy but as far as I know there's no real good answer to this, yet)
And what is the nature of space-time that makes it "bendable".

That's the thing: spacetime isn't bent. That's why it's important to know the difference between a straight line in a cartesian space and what a geodesic is. If you go by the 'straight line/cartesian' POV then space (not spacetime!) is bent. But if you look at what a geodesic is then you will notice that spaceTIME is straight.

Apr 27, 2016
DS: Newton's Bucket is addressed by the "Mach principle" https://en.wikipe...rinciple within the context of General Relativity. It's not that you need gravitation from these other distant objects, it's that other objects provide information on what an inertial reference frame is.

Second, the Casimir effect has nothing to do with space-time and everything to do with electromagnetic fields. In the simplest, but somewhat inaccurate, picture we can paint, between two metal plates, only some small subset of photons can be created, virtually or otherwise. Outside of the two plates, any number of photons may exist. In this, again inaccurate, picture, it's the external 'virtual' photons pushing on the plate, not anything to do with space-time.

Apr 27, 2016
DS: continued:

As to 'accelerating' you're accelerating compared to what you yourself were a moment ago. Two observers in relative motion measure space and time differently right? Imagine two balls flying along side each other at a constant speed (equivalently, at rest). One is 'kicked' by some outside force and changes its speed. These two balls now are in relative motion and observe space-time differently from one another. You can then reduce it to one ball and how it measures the universe compared to how it used to measure the universe a moment before.

In GR we call this "Momentarily Comoving Rest Frames." Instead of trying to solve a continuous acceleration, we imagine motion as constant v, small kick to new v, constant, kick, etc. and then apply differential calculus to the result to obtain the continuous case.

Apr 27, 2016
@torbjorn
The vacuum energy in the Casimir effect should be (has not been verified yet) to be the zero-point energy of the particle fields. [ https://en.wikipe...r_effect ] Same goes for dark energy in cosmology (also not verified).
Technically, the vacuum energy in the Casimir Effect has been verified calculationally to be the zero-point energy of quantum mechanics; however it is correct to say that there remain calculational problems relating it to dark energy, and it is also correct to say that although most cosmologists identify the dark energy with the cosmological constant from GRT, that also remains a matter of debate.

In other words, these effects should fit Wilzsek's Core Theory (now that the Higgs has completed the Standard Model of particles) or what used to be called the semiclassical approximation (quantum field theory of all particle fields + gravity).
Yes.

[contd]

Apr 27, 2016
[contd]
Spacetime may curve but it hasn't been 'bent'.
Colloquially, in the manner I think @dejesusluisx meant the term, they're pretty much equivalent. To me this is just an argument about semantics; I'll go with "matter tells spacetime how to curve, and spacetime tells matter how to move."

I had no further quibbles or illuminations to add to your other statements and agree with them pretty much.

Apr 27, 2016
But measuring spacetime 'itself' is tricky. It's not a 'thing'. It's an environment for things to be in. It's geometry - not particle physics.
Hmmmm, I disagree on the same grounds I did when @shavera said this. I think there are good definitions of what spacetime is in both relativity and QM. I'll discuss that more with him in the next few posts.

And what is the nature of space-time that makes it "bendable".

That's the thing: spacetime isn't bent. That's why it's important to know the difference between a straight line in a cartesian space and what a geodesic is. If you go by the 'straight line/cartesian' POV then space (not spacetime!) is bent. But if you look at what a geodesic is then you will notice that spaceTIME is straight.
That ignores gravitational time dilation. Gravity and acceleration warp both space and time, together. Also, I've just about given up talking about space as if it were somehow separate from time.

Apr 27, 2016
@shavera
DS: Newton's Bucket is addressed by the "Mach principle" within the context of General Relativity. It's not that you need gravitation from these other distant objects, it's that other objects provide information on what an inertial reference frame is.
This seems rather a circular definition. The problem with it is that this is essentially the implicit claim that you cannot define rotation in an empty universe with no matter except one object. If that object is extended, and one cannot define rotation, what happens to the angular momentum of its extended parts? Angular momentum is conserved. That's a nasty little conundrum. Whereas if you accept that spacetime itself is a thing, albeit not a material thing, then you have no problem like this.

As far as it being the gravitation from those distant objects, in GRT the gravity field itself is what defines spacetime; to put this another way, it is that which can be curved without material presence.

[contd]

Apr 27, 2016
[contd]
To put this in the context of the empty universe, and GRT, the metric can be perfectly flat, yet the cosmological term can give spacetime in an empty universe curvature nevertheless; and even if all three terms in the Einstein Field Equations are flat, a gravity field of zero is not "no gravity field" if spacetime is a thing. That would be like claiming there will be no weather tomorrow.

Second, the Casimir effect has nothing to do with space-time and everything to do with electromagnetic fields. In the simplest, but somewhat inaccurate, picture we can paint, between two metal plates, only some small subset of photons can be created, virtually or otherwise. Outside of the two plates, any number of photons may exist. In this, again inaccurate, picture, it's the external 'virtual' photons pushing on the plate, not anything to do with space-time.
The problem with this view is that it is not only photons.

[contd]

Apr 27, 2016
[contd]
It is all possible virtual particles: photons, weak bosons, gluons, and (presumably) gravitons as well. All have wavelengths, and all possible wavelengths can exist outside the plates, but not between them (except (putative) gravitons, to which matter is transparent). Furthermore, the photon interaction is insufficient to explain the measured pressure; only when the rest of the possible vacuum fluctuations are taken into account is the measured pressure accounted for.

This is a very serious problem with claiming that it's "only electromagnetic."

Apr 27, 2016
@shavera
As to 'accelerating' you're accelerating compared to what you yourself were a moment ago.
No, you're accelerating the same as you were a moment ago. You measure no difference. But you *can* measure the acceleration. And you *always* can measure the acceleration, even if you can't see outside; but you cannot measure the *speed* without looking outside if it doesn't change. In fact, SRT says that all inertial frames are equivalent, and this means that you're completely justified in stating that you are at rest and the universe outside is moving past you, rather than the other way 'round, as long as you're not accelerating. However, you are *not* justified in stating that you are not accelerating if you can measure it locally. I repeat, motion is relative, but acceleration is absolute. And I ask again, if acceleration is not relative to spacetime, then what is it relative to?

[contd]


Apr 27, 2016
[contd]
Two observers in relative motion measure space and time differently right?
You mean two inertial observers here.
Imagine two balls flying along side each other at a constant speed (equivalently, at rest). One is 'kicked' by some outside force and changes its speed.
That's not what we're talking about. This is a Lorenz boost; but we're talking about continuous acceleration. Completely different things. I left out the rest for brevity; I'll address it below.

In GR we call this "Momentarily Comoving Rest Frames." Instead of trying to solve a continuous acceleration, we imagine motion as constant v, small kick to new v, constant, kick, etc. and then apply differential calculus to the result to obtain the continuous case.
OK, you can do that, but the question remains, you're still changing velocity, you can still measure it, and you still haven't defined what these continual small kicks are relative to...

[contd]

Apr 27, 2016
[contd]
and why, unlike continuous motion, we can measure them locally. The answer is, to my mind, that we are accelerating with respect to local spacetime. That is, with respect to the local curvature of spacetime. And I mean "curvature" in its broadest sense, in which zero curvature is still a curvature, just as a straight line on a Cartesian graph is still called a "curve" even though in colloquial language, it is not curved at all.

Apr 27, 2016
Then there's the Casimir Effect. Empty space pushing two plates together. What's pushing?

The Casimir effect is the radiative version of Van der Waals interaction. The field originates from the electronic degrees of freedom of the plates.

This is incorrect, according to QM, because you have not included other virtual particles besides photons that the vacuum can create. Measurements are very sensitive, but not yet sensitive enough to differentiate whether the relatively weaker (because less common) higher energy virtual particles produced by the vacuum make a contribution beyond that calculated for electromagnetism alone.

Apr 27, 2016
@Da Schneib
You are now talking about virtual particles. The range of such interactions is extremely short, namely equal to the Compton length. For an electron this is 2 picometers and forget neutrino's ;-) .
So we can safely and totally ignore this.
Errr, even if we only consider electromagnetism, we are still considering virtual particles as the producers of the force, according to the main interpretation of the cause of the effect. You're arguing against your own viewpoint. The dispute iin the mainstream about the Casimir effect is about whether there are additional forces besides electromagnetism that affect the magnitude of the force, not about its source. Outside the mainstream there are a few left who argue against vacuum pressure due to virtual particles, but they also argue against virtual particles in the first place.

Apr 27, 2016
@Phys1
Nowadays Casimir force analysis is required for the design of MEMS, so it has evolved from esoteric field theory into down to earth engineering!
Now that is definitely interesting! Sounds like I need to hunt up some links and do some research. If you've got any handy I'd be much obliged to you.

BTW I should note that I got this view of the Casimir effect from Susskind(2005) "The Cosmic Landscape" which I recommend to everyone's attention.

I should also note that Casimir himself was looking for van der Waals forces with his experiment (and developed it for that purpose) and found something anomalous but apparently very interesting to QM theorists in the context of deeper QM.

@Hat, thanks, we can be polite even if we disagree. Finding people who are willing to do that is a good guide to who's worth talking to, I find. When someone's right, they're right, and when they aren't (and when I'm not) they learn something, if they have a good attitude.

Apr 27, 2016
Never in human affairs have so many known so little and yet spewed so much bullshit. This site really loves to pander to its trolls.

Dumb shits, we don't care what your gut feeling is. No one comes here to see what compost has to say or what dumbrobertson "expects". lol How fucking arrogant is it to say that you have no background in the field and then enlighten us as to what you expect the result to be?

Die and have an invitation sent to us to dance on your grave and THAT we will care about. The rest of the time you're as appreciated, and predictable, as flies at a picnic.

- antigoresuckpuppet

REPORTED FOR ANTISOCIAL, PSYCHOPATHIC AND DEMONIC BEHAVIOR.
YOU SOUND LIKE A WHITE-SUPREMACIST AND NEO-NAZI.
TAKE YOUR HATE-MONGERING TO STORMFRONT.ORG WHERE IT WILL BE APPRECIATED.

Apr 27, 2016
DS: I understand what you're arguing, and I'm just trying to say that the arguments you're raising were raised at the very beginning of GR and have long been considered resolved. If you're actually interested in the answers, there's plenty out there to read on those questions.

Mach's principle isn't circular, it's a foundational principle of General Relativity. All measurements only exist with respect to other objects in the universe. There's no fixed reference frame.

Acceleration is functionally a lot of Lorentz boosts stitched together. The maths work out really well, and I invite you to explore them. You're correct about always being able to measure acceleration and the reason why is because your new reference frame is different than the one you used to occupy. Read about Momentarily Comoving Rest Frames for more.

Apr 27, 2016
@shavera, I see that you have misunderstood my argument on Mach's principle. I don't really care if it's supposedly foundational. I'm pretty disappointed that you seem to think I'm arguing for a fixed reference frame; that's why I know you didn't understand what I said.

And I'm well aware of the clock postulate and the treatment of acceleration in SRT using MCRFs. I think you've completely missed the point that this implies about the equivalence principle and what acceleration really means in physical terms.

I don't think you've answered my arguments. If you aren't interested enough to think about it, it's no skin off my posterior.

I see dismissive answers like yours as a problem in science generally. You got a 3 for that. Sorry, man, I calls 'em like I sees 'em.

Apr 27, 2016
And BTW, @shavera, you might want to read up on Mach's principle a bit:

The idea is that local inertial frames are determined by the large scale distribution of matter, as exemplified by this anecdote:

You are standing in a field looking at the stars. Your arms are resting freely at your side, and you see that the distant stars are not moving. Now start spinning. The stars are whirling around you and your arms are pulled away from your body. Why should your arms be pulled away when the stars are whirling? Why should they be dangling freely when the stars don't move?

Mach's principle says that this is not a coincidence—that there is a physical law that relates the motion of the distant stars to the local inertial frame. ... A very general statement of Mach's principle is 'Local physical laws are determined by the large-scale structure of the universe.'"


https://en.wikipe...rinciple

I think you've far overstated the importance of it to GRT.

Apr 28, 2016
The origaninaly established order in the universe which is supported by precisely tuned physical laws, constants and fundamental forces, can not be defined without asbsolute references - absolutes that can not change with time and position in the physical world.
All discussionс and speculations on this theme is worthless clpatrap.

So the GR is one of many modern mitologies introduced in socienty with specific purpose. In this case to justify double standards (moral relativism - lawlessness) in society by represent it as something that naturaly occurs in nature.

Apr 28, 2016
There's no fixed reference frame. […] Read about Momentarily Comoving Rest Frames [MCRF] for more.

That is what I believed until I [realized] the cosmic microwave background constitutes such a frame.


The CMB is a MCRF, and is no different than any other frame wrt the form of the laws of physics. It is effectively arbitrary, meaning merely [mathematically] convenient for the given cosmological problem.

To show that space and time are "things unto themselves",…. you would have to show how they are involved in dynamics,… i.e. as a time-particle or a space-particle, or a s/t-force, or a measurable s/t-field.

IOW, relativity makes use of space and time as a kinematical theory,… not a dynamical one.


Apr 28, 2016
Einstein imaged a version of Newton's Bucket, with two relatively and spinning spheres of liquid (with observers fixed with them), where one is oblong wrt the axis of spin while there other is not. Referencing Mach's Principal, he stated,…

"No answer can be admitted as epistemologically satisfactory, unless the reason given is an observable fact of experience. The law of causality has not the significance of a statement as to the world of experience, except when observable facts ultimately appear as causes and effects." – Einstein

…..

Apr 28, 2016
Supporting Mach's principal, is Pfister and Braun having demonstrated that the water surface in a bucket of water NOT spinning relative to the distant stars, would become concave if placed inside a hollow sphere which WAS spinning. This is due to frame dragging, the Lense-Thirring effect.

Now, is frame-dragging an indication or a statement that space-time is a substance or ontologically Real in some way?

No, ….it is a statement of how the presence of mass-energy effects of the metric-tensor at each point of interest. The purpose of the metric-tensor is to define some meaning of a "straight-line", …a geodesic, and so the path for which objects have NO FORCE effecting them. This is a coordinate free concept given the nature of tensors. For extended objects, the divergence of geodesic paths at each point, give the tidal-forces.


Apr 28, 2016
I'm not being dismissive, I'm trying to say that you're being pretty casually dismissive of arguments that have been made long ago. If you're intellectually honestly interested, there are a lot of more formal places to learn about these topics than I have time or space to write in a forum post. That's just inherent to the nature of communication like this; I can only give a brief snippet of larger arguments that have been made more generally.

The brief outline is that General relativity does not treat space-time as a thing, it treats it as a mathematical set of measurements. When we talk of "curvature" that's a term that gets abused in popular press. There's not a "fabric" that gets "warped" in the presence of mass. The curvature is in a maths sense of how one measures distances and angles and times changes in a way that can be described in a particular field framework. (cont.)

Apr 28, 2016
Newton's bucket is resolved by saying in a universe with only a bucket there's no real distinction between a rotating bucket or a rotating universe. They both end up with the same result (the fictitious force known as 'centrifugal'). Without anything else in the universe, there's no meaningful way to tell the difference. However the moment a second object comes into existence anywhere in that universe, it's trivial to check if that object is also experiencing the apparent centrifugal force. If it's not, then you can distinguish whether the universe is rotating or the bucket.

The reason you can detect acceleration is very simply because you're changing inertial reference frames. Even if it's continuous, not stepped change, that variation from moment to moment in how you measure length and time changes how you describe the physics of some body. That change in the physics can be observed and measured.

Apr 28, 2016
There's no fixed reference frame.

Hi Shavera
That is what I believed until I realised the the cosmic microwave background constitutes such a frame. The data as generally presented are corrected for a speed of 627 km/s of the sun in the direction of l= 276°±3°, b = 30°±3°. So not only can we locally measure absolute acceleration, with a bucket, but also speed with a Planck.
https://en.wikipe...isotropy
Hmmm, @Phys1, you gotta be real careful with this. Because of the fluctuations in the CMB, we know that there will be fluctuations in the CMB frame throughout space. It therefore cannot serve as an absolute frame, only a local one.

Apr 28, 2016
I'm not being dismissive, I'm trying to say that you're being pretty casually dismissive of arguments that have been made long ago.
Well, I'm not ever casually dismissive of much of anything; I look things over before I dismiss them. Thanks, however, for clarifying your intent and I'll accept that rather than get shirty and demand an apology; and I'll even say I'm sorry for the misunderstanding.

The rest will have to wait; work to do. Look for something later today.

Apr 28, 2016
To show that space and time are "things unto themselves",…. you would have to show how they are involved in dynamics,… i.e. as a time-particle or a space-particle, or a s/t-force, or a measurable s/t-field. IOW, relativity makes use of space and time as a kinematical theory,… not a dynamical one.

To elaborate on this,… the nonlinearity of the GR field equations would certainly imply 'dynamics' given gravitational-waves, however, GR still only describes the metric tensor at each point which is used to establish a notion of lengths and times. It is still only a geometry (Riemannian manifold). A quantum theory of gravity would make use of the graviton as a particle that would represent the 'substance' of gravity.

........................

EDIT: The purpose of the metric-tensor is to define some meaning of a "straight-line" [by use of the geodesic equation].


Apr 28, 2016
,..... but I still see no physical Time or physical Space in terms of some force or entity of some sort, involved in dynamics itself,.... but rather only as Operationally Defined (As Einstein did so in SR/GR),... which is to say,... "time" is defined to be represented as some physical system, which in turn is affected by the presence of mass-energy.


Apr 28, 2016
The Einstein field equations only states that the metric-tensor* is proportional to the presence of mass-energy, at each point. It does not say WHY, but only just that it IS. IOW a geometry expressing MCRF and is what I meant by kinematics.

To go beyond this, into statements about the ontology of space and time, is to enter into interpretations of theory, which is properly the domain of philosophy of physics. Some would make such ontological interpretations all the while claiming that philosophy has nothing to do with physics.

*[The Riemann tensor, which is expressible in terms of the metric-tensor; The curvature is of a mathematical space, the Riemann manifold; GR can have a space-time coordinate-free representation]

Apr 28, 2016
That does not alter the fact that CMB represents an absolute rest frame.


Generally when one uses the word "absolute" wrt inertia reference frames they are referring to a preferred coordinate basis in which the principal of general covariance does not hold, thus violating the fundamental postulate of relativity. I doubt that you mean this however.


Apr 29, 2016
Interesting that the moderator shows up to delete a comment that is anti-troll, and WAY short of the kind of personal abuse that Stumpy or Otto posts about gkam. More evidence that the site is actively encouraging trolls.

Apr 29, 2016
It's beyond that. Click on the name. The account has been deleted. If that doesn't spell it out pretty clearly I don't know what does. Think of the people on here promoting policies that will kill thousands, the intimate, constant personal abuse, the irrelevant non-sense, the outright spam...but someone that says they'll dance on their enemies' grave- none named- is instantly deleted.

This site has gotten to the point that only a troll WOULD post here. Not being one, I'm shoving off. Thanks for the fish.

Apr 29, 2016
And how feckless is obamasucker, quoting the whole terribly offensive post...so that it still exists.

WTF is "demonic behavior" anyway? Yeah, none of his crap has ever been deleted and it is abusive, wrong, irrelevant and offensive. Like I said...

Apr 29, 2016
It's beyond that. Click on the name. The account has been deleted. If that doesn't spell it out pretty clearly I don't know what does. Think of the people on here promoting policies that will kill thousands, the intimate, constant personal abuse, the irrelevant non-sense, the outright spam...but someone that says they'll dance on their enemies' grave- none named- is instantly deleted.

This site has gotten to the point that only a troll WOULD post here. Not being one, I'm shoving off. Thanks for the fish.

LOVE yer thanks for all the fish reference...:-)
Actually, I think removal is based on the number of "report" buttons clicked..

Apr 29, 2016
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Apr 29, 2016
AGreatWhopper

5 /5 (5) 4 hours ago
It's beyond that. Click on the name. The account has been deleted. I


You cannot be serious. Totally lightweight no seriousness account, but compared to the endless spammy spew of antirational, bsht, OS, etc., that is really incredible. OK. I finally buy that the site is paid not to delete conservative trolling. I get the thing about popularity and a post being deleted, but- have I missed it?- I can't remember a post ever being deleted on that account by the moderator. Pretty mild comment, considering, and the account is terminated?!? I can't think of another explanation. Pretty sad.

Apr 29, 2016
@Nuomenon:

"A quantum theory of gravity would make use of the graviton as a particle that would represent the 'substance' of gravity."

You are objectifying too eagerly. GR is a perfectly OK linear quantum field theory at low energies, you can derive the graviton without any deeper knowledge as per the usual Lagrangian.

"It's often said that it is difficult to reconcile quantum mechanics (quantum field theory) and general relativity. That is wrong. We have what is, for many purposes, a perfectly good effective field theory description of quantum gravity. It is governed by a Lagrangian ...

In other words, as an effective field theory, gravity is no worse, nor better, than any other of the effective field theories we know and love.

The trouble is that all hell breaks loose for ε∼1. Then all of these infinite number of coupling become equally important, and we lose control, both computationally and conceptually."

[tbctd]

Apr 29, 2016
[ctd]

[ https://golem.ph....639.html ]

In other words, beyond the facile description of spacetime curvature (with or without a graviton field coupled to it), we can't yet objectify gravity.

Since I am interested in astrobiology, I note that the same problem happens for life. We can't define it very well, but we can study how it behaves. It is a very common state of the art in science. I wouldn't worry about it.

Especially if, as your handle suggest, you are more interested in the fantasies of philosophy instead of the facts of science. E.g. you may have a platonian belief system that objects are things in themselves, and not simply naturally persistent patterns of wiggles in particle fields. (Laws are other types of persistent patterns.)

Except possibly that gravity and so cosmology (universes) are different . Stay tuned!

Apr 29, 2016
From another thread, the trolls are going for even more. PO isn't troll friendly enough yet. To whit:
Noumenon

1 /5 (7) Apr 26, 2016

I am downvoted by the usual psychos. The ignore button would be more functional if it also eliminated the trolls from voting.

Please send Phys.Org a request to disable comment ratings. Their associate site has done this.


A troll's dream come true. [...]. I can't believe most the trolls wouldn't love that.


?! The first sentence was posted by Phys1, I followed with the 2nd.

If Phys.Org would disable comment ratings then there is no way an idiot-troll could possibly effect legitimate posters here because of the Ignore feature.

Look at my ratings in this very thread.... legitimate knowledgeable contributions to the discussion yet 1-rated by the following trolling dolts.....

john berry_hobbes
AGreatWhopper
jim_xanara
chileastro
BongThePuffin

"conservatives" ? tells me everything I need to know.


Apr 29, 2016

?Phys1

Given politico-economical system is based om believes and moral standard of majority of people in this system. So to be supported the idolatory system warshiping the golden calf is needed to be supported atteism, consumerism and anti chistian attitudes in society. This is done by intoduction and constant maintenance of modern mythologies in society by social engeneering, which are named science ragradless of their unscientific nature and violation of scientific principles.
It is simple as usual.

Apr 29, 2016
A persons comment should stand on its own individual merit,.... until someone who is not an intellectual coward hiding under their desk, makes a counter argument. Phys.Org installed the IGNORE option,... so this is the means in which you avoid being effected by posters who you're not competent to object to.

The only reason for the rating system given the IGNORE feature is for people to prevent others from reading comments they don't like,.... rather than leaving it up to them to decide.

My above comments and those in other threads did not deserve a pack of 1-ratings, especially given they were factual and based on their individual merit,.... so clearly we have abuse of the rating system by someone that does not like me for out of context reasons and YET will not use the IGNORE feature.

To make such idiot-trolls irrelevant REQUIRES the comment ratings to be disabled, or at least implementation of Phys1 idea.


Apr 29, 2016
...Especially if, as your handle suggest, you are more interested in the fantasies of philosophy instead of the facts of science. E.g. you may have a platonian belief system that objects are things in themselves, and not simply naturally persistent patterns of wiggles in particle fields. (Laws are other types of persistent patterns.)


Thank you for your response.

If you have read with any competency any of my posts wrt philosophy of physics or my use of Kant, you would almost have to go out of your way not to notice that my arguments are in fact very much anti-metaphysics in science. In fact my comments above were to support shavera's post questioning the notion of a "real" substantive space-time. How was this missed? Why presume such wild speculation wrt what my thoughts are. I post on science facts here,.... and anti-realism in science. Your "characterization" of me is not based on your understanding nor facts.


Apr 29, 2016
All the evolutional processes (physical and biological) without the ideas, will, knowledge, technological capabilities and action of purposeful intelligent being are physically impassible because violate the natural laws for the information.
The Information is non material fundamental entity which is independent from the matter and energy. It can not spontaneously arise from matter and energy which obey the established physical laws. Matter and energy can be used only to store or transfer the existing information but not to generate it. It does not exist physical laws or natural processes in nature that can cause the increasing of the order (information) in the physical systems .

Apr 29, 2016
The information represent the ideas and will of intelligent being and is transfered always to recipient who or which is able to understand it. This is done by the agreement between the sender and recipient which includes set of rules for coding and decoding of the information for it right understanding. Without this coding and decoding rules, which are product of intensional choice, the information is useless. The new information and it coding and decoding rules can arise only by mental process of intelligent being. All given chain of information ca be tracked back to its intelligent source.


Apr 29, 2016
Since the complexity and density of information recorded in DNA (the material carrier of biological information) is million of times greater than the all technological achievements of people nowadays, it must originate from super intelligent being. Since the information is not material entity the intelligent source of information product of mental process must have at least non material component - spirit.

Apr 29, 2016
@Noumenon
Above I state that there is a universal rest frame, namely that of the cosmic microwave background. That goes against at least the spirit of special relativity.
What would Kant say ?
Anybody else have a well founded opinion on this?
I hear mostly silence.


What Kant would say is not of relevance here. I was responding to Torbjorn's baseless accusation .

I made posts above in response to you.

Apr 29, 2016
That does not alter the fact that CMB represents an absolute rest frame.


Generally when one uses the word "absolute" wrt inertia reference frames they are referring to a preferred coordinate basis in which the principal of https://en.m.wiki...variance does not hold, thus violating the fundamental postulate of relativity. I doubt that you mean this however.


Whether it violates principles or not, I claim that it is an observed fact.


It is a useful reference frame. I don't think anyone is disputing that. Wasn't the line of argument about the notion that space and time were "things", or did I lose track? Wasn't that your point in mentioning a CMBR based frame?

If so, then this frame is no more special, with respect to the principles of GR, than any other reference frame, (apart from mathematical convenience given the nature of the problem). It is not a physical indication of substantive nature of space-time.


Apr 29, 2016
Newton's bucket is resolved by saying in a universe with only a bucket there's no real distinction between a rotating bucket or a rotating universe. They both end up with the same result (the fictitious force known as 'centrifugal').

This solution does not address the fundamental question whether acceleration has physical meaning in an otherwise empty universe. That is the question Mach sought to answer.

Anybody have an opinion on this?
If not you have to ask yourself what you are doing here.

At Last! A request for opinion, not data!
This Universe is in motion relative to either in another medium or just in, and of, itself. That motion is what originates all other processes, forces, matter, etc WITHIN it's "field".
Why can't space be in motion relative to other space?
Anyway, you asked for it - Just my opinion...

Apr 29, 2016
@viko_mx
"the agreement between the sender and recipient"
So you know this. Then why don't you live by it?

He thinks he does...

Apr 29, 2016
Regarding Newton's bucket.... and Mach's principle .... I provided an actual experiment above that I thought resolved the question(?)

We spin the bucket. A) Initially the bucket is rotating relative to the water (as the water is not rotating yet), and there is no centrifugal forces B) Soon the friction transfers rotation to the water as well so that the bucket and water are no longer rotating relative to each other and yet centrifugal forces occur causing the water to climb the walls.

For Newton, A) meant there was no centrifugal forces produced with relative rotation, while B) meant there was without relative rotation,.... so that this supports the notion of absolute space (more correctly justifies his use of that postulate for his Principia)

.....

Apr 29, 2016
.....

Mach suggested that had the bucket walls been increased in mass, the results would have been different.

Above, I referenced such an arrangement that has actually been performed (or calculations, or see Lense-Thirring ),... where the bucket is not spun relative to the fixed stars, but instead a hollow sphere is spun around the bucket instead,.... producing centrifugal forces in the water !

Einstein was initially greatly influenced by Mach's philosophy for the development of GR, but as GR developed eventually Mach's ideas became superfluous as the problem became answered in the structure of the mathematical formalism of MCRF already mentioned by shavara above.


Apr 30, 2016
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Apr 30, 2016
The question remains unanswered what the bucket experiment would give in empty space,
or in a space with only the Earth to determine the flat surface.


I would agree with that. But since it's not possible to arrange such an experiment (see Einsteins quote above), it is more philosophy than physics, albeit just as interesting question. Upon further investigation there does not seem to be a consensus on the Mach principle, which may have to do with operationally defining it. If defined as being represented in the above referenced experiments, then it is resolved imo.

................

[I guess Torbjorn is hiding under his desk]


Apr 30, 2016
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Apr 30, 2016
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Apr 30, 2016
@Phys1, sorry I been busy.
Since the CMB is believed to be tightly related to the primordial universe, the universe has a rest frame, unless ofcourse the CMB looks different from place to place as you suggest.
But in order to find out exactly what that rest frame is, we'd have to visit lots of other galaxies, and we can't do that, at least without an FTL drive. Right now, we can't even visit other stars.

By assuming most galaxies and galaxy clusters are approximately at rest in their own local CMB frames, we can define an approximate universal rest frame, but we can never define a precise one. And this is theoretical physics, so if there's no precise one, there isn't one. The closest we can come is to say that we can define a *local* CMB rest frame. And that is what your example has done: define the local CMB rest frame of the Local Group.

Apr 30, 2016
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Apr 30, 2016
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Apr 30, 2016
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Apr 30, 2016
@shavera, busy day yesterday. Finally getting to this.

The brief outline is that General relativity does not treat space-time as a thing, it treats it as a mathematical set of measurements. When we talk of "curvature" that's a term that gets abused in popular press. There's not a "fabric" that gets "warped" in the presence of mass. The curvature is in a maths sense of how one measures distances and angles and times changes in a way that can be described in a particular field framework.
When you say things like this, a couple points come to mind:
1. I'm not talking about how GRT treats it. I'm talking about how it is.
2. I think you're far too caught up in the definition of "a thing" as "something material." I'm not talking about anything material, or of substance; I'm talking about spacetime itself.
[contd]

Apr 30, 2016
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Apr 30, 2016
[contd]
I don't see any contradiction in saying that while spacetime can't provide an absolute reference frame for motion, it can for acceleration, particularly when we consider the clock principle. Let's think about exactly what the clock principle and equivalence principle jointly imply:

According to the clock principle, all the effects of net linear acceleration can be accounted for as SRT effects due to motion. There is no additional component that GRT adds to this to account for some special thing acceleration does.

But gravity and acceleration are equivalent; and this implies that the net gravity field, when it is not flat, is the same sort of thing as all those infinitesimal Lorenz boosts that make up an acceleration in a net zero gravity field. In other words, if acceleration is absolute, so is gravity.

[contd]

Apr 30, 2016
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Apr 30, 2016
[contd]
Now, @Phys1 has made a pretty good case for the CMB reference frame. Not one we can actually ever measure for the whole universe; but at least one that seems to define a local average reference frame that we can measure motion against. So now, we can see that we can come arbitrarily close to such a reference frame, though it is not universal, only local.

And this makes sense; the net local gravity field defines this frame, and this is the frame in which net local acceleration makes sense. Both are defined in terms of net local spacetime; and this is how and why acceleration and gravity are equivalent.

Without accepting spacetime as a "thing," none of this makes any sense at all. Not a material thing; not aether; not a universal absolute spacetime. A local absolute spacetime, that varies from place to place, because the total gravity field varies from place to place.
[contd]

Apr 30, 2016
[contd]
This makes the exact, complete gravity field at any point its absolute reference. And that makes spacetime a thing, because without it we cannot have a gravity field; spacetime is that which gravity fields are imposed upon.

You cannot define an absolute background for the whole universe against which motion can be defined; true. But you *can* define a *local* absolute background against which *gravity and acceleration* can be defined, and we see that from the fact that there is a definable CMB frame. And from the fact that there is a definable curvature at each point in spacetime, the stress-energy tensor, which varies from point to point. This makes spacetime a thing; as I said before, spacetime is the thing which is curved in a manner varying from point to point according to the precise stress-energy tensor at each point.

[contd]

Apr 30, 2016
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Apr 30, 2016
[contd]
Other points must exist with the same stress-energy tensor; thus, there is no absolute way to determine which point you might be at. Other points even with the same collection of stress-energy tensors at points surrounding them, to an arbitrary distance, must also exist; thus, there is no absolute definition of location or motion in spacetime. But locally, even in the weak limit, there is no particular reason that a collection of points with the exact same variance over a field should exist, and in fact it is extremely unlikely that it should, moreso the larger our collection of points is; thus, locally, we can define a location, and this fits with our ability to measure such a location. For example, in the Milky Way galaxy, 33,000 light years out from the galactic center, on a small planet we call Earth circling a fairly average star we call the Sun.

Apr 30, 2016
@Phys1
If the CMB frame would depend on cosmological position, then it is local not cosmological.
Precisely. There is no absolute location, nor absolute CMB frame. There is only local location, and a local CMB frame. We can see this due to the fluctuations in the CMB, implying fluctuations in the CMB local rest frame.

I wouldn't be parsing this so heavily except that's what the phenomena we see-- and those we cannot-- appear to dictate.

We can define a precise one, but we cannot observe it to infinite precision. No issue there.
We can define a precise one for any location we can visit, but we cannot know it for locations we cannot. The bigger your patch size is, the more imprecise your integration of the field is compared to any particular point within it. The more precise you become, the smaller your patch size must be, confirming that this is a local effect not a global one. If it were global it would be precise over any size field.

[contd]

Apr 30, 2016
[contd]
And this is theoretical physics, so if there's no precise one, there isn't one.
Be careful, you just argued that there is no universe.
No, I just argued there is no universal absolute rest frame; only a local absolute rest frame, defined by the local CMB rest frame. Like I said, this is theoretical physics; if there is no universal absolute rest frame, there is no absolute rest frame, by the definition of absolute rest frame used in SRT, which definition GRT inherits.

The closest we can come is to say that we can define a *local* CMB rest frame. And that is what your example has done: define the local CMB rest frame of the Local Group.
I don't understand why you implicitly advance the idea that the CMB is not cosmological but local.
I don't mind but you should state it up front.
Because the variations in the CMB indicate that it has no universal absolute rest frame and cannot.

Apr 30, 2016
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Apr 30, 2016
There's not a "fabric" that gets "warped" in the presence of mass. The curvature is in a maths sense of how one measures distances and angles and times changes in a way that can be described in a particular field framework. - shavara


When you say things like this, a couple points come to mind:
1. I'm not talking about how GRT treats it. I'm talking about how it is.


There one and the same,.... as GR represents present understanding..... You're speaking philosophy here.

Without accepting spacetime as a "thing," none of this makes any sense at all. Not a material thing; not aether; not a universal absolute spacetime. A local absolute spacetime, that varies from place to place, because the total gravity field varies from place to place.


At any given such point, there are an infinite number of geodesic paths through it, so again there is no preferred coordinates.


Apr 30, 2016
Newton's bucket is resolved by saying in a universe with only a bucket there's no real distinction between a rotating bucket or a rotating universe. They both end up with the same result (the fictitious force known as 'centrifugal'). Without anything else in the universe, there's no meaningful way to tell the difference.
This looks to me like someone maximally violating Occam's Razor in order to avoid something that appears to disagree with their interpretation.

It is far simpler to assume a rotating object than it is to assume a rotating universe. Furthermore, we've seen lots of rotating objects, and never seen a rotating universe, and proposing it by definition assumes that there is some outside frame of reference against which the universe can be said to be "rotating."

[contd]

Apr 30, 2016
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Apr 30, 2016
[contd]
To top it all off, using your own logic, the moment some other object comes into existence it is possible under your scenario that we would not find that the original object was rotating, but that the universe was. And if it were and could, then you have immediately defined a universal absolute frame of reference, violating your postulates maximally.

I'd say that's pretty much QED.

The reason you can detect acceleration is very simply because you're changing inertial reference frames.
No, the reason you can detect acceleration is that you are moving between points of different values of the stress-energy tensor. Which is exactly how you can detect you are moving in a gravity field between points of different gravitational potential.

[contd]

Apr 30, 2016
[contd]
To top it all off, using your own logic, the moment some other object comes into existence it is possible under your scenario that we would not find that the original object was rotating, but that the universe was. And if it were and could, then you have immediately defined an absolute frame of reference, violating your postulates maximally.

I'd say that's pretty much QED.

The reason you can detect acceleration is very simply because you're changing inertial reference frames.
No, the reason you can detect acceleration is that you are moving between points of different values of the stress-energy tensor. Which is exactly how you can detect you are moving in a gravity field between points of different gravitational potential.

[contd]

Apr 30, 2016
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Apr 30, 2016
[contd]
Even if it's continuous, not stepped change, that variation from moment to moment in how you measure length and time changes how you describe the physics of some body. That change in the physics can be observed and measured.
But it's not a variation from moment to moment in how you measure length and time unless you agree there is an absolute frame of reference against which to measure them.

In this case I argue that there is a local absolute frame of reference; and resolve the paradox that is implicit in your thoughts by stating that there is a local one but not a universal one.

And I point out yet again that this local absolute frame of reference is the stress-energy tensor varying from point to point, which variation prevents it being a universal absolute frame of reference prohibited by the postulates of SRT and GRT.

And this agrees with the view that spacetime is a thing.

Apr 30, 2016
It's beyond that. Click on the name. The account has been deleted. If that doesn't spell it out pretty clearly I don't know what does. Think of the people on here promoting policies that will kill thousands, the intimate, constant personal abuse, the irrelevant non-sense, the outright spam...but someone that says they'll dance on their enemies' grave- none named- is instantly deleted.

This site has gotten to the point that only a troll WOULD post here. Not being one, I'm shoving off. Thanks for the fish.

LOVE yer thanks for all the fish reference...:-)
Actually, I think removal is based on the number of "report" buttons clicked..
LOL, this is reminiscent of the definition of Hell as a place where a bunch of people are up to their noses in sewage chanting "Don't make waves."

Apr 30, 2016
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Apr 30, 2016
The reason you can detect acceleration is very simply because you're changing inertial reference frames. - shavara

No, the reason you can detect acceleration is that you are moving between points of different values of the stress-energy tensor. Which is exactly how you can detect you are moving in a gravity field between points of different gravitational potential.


If you move along a geodesic you will not experience acceleration at all *, ... and if you are not moving along a geodesic you are experiencing acceleration because some arbitrary thing is interacting with you.

* excepting for extended objects where the divergence of geodesic produce tidal forces.

A better argument to substantiate an ontology of space-time would be to ask shavara how gravitational waves carry energy. :)


Apr 30, 2016
.... there are no 'local absolute frames of reference', and there are no 'universal absolute frames of reference',.... as this would violate https://en.m.wiki...ariance, as this would imply some preferred coordinates,.... undermining GTR. There can be accelerations induced by the choice of coordinates,.... which is why coordinate-acceleration is distinct from proper-acceleration.

[of course its ok if some speak philosophically, but if Noumenon does than that bad,... tables turned :)]

Apr 30, 2016
[contd]
And this is theoretical physics, so if there's no precise one, there isn't one.
Be careful, you just argued that there is no universe.
No,

Your argument overshoots its mark greatly. You argued that because the CMB restframe can not be determined with absolute precision, it does not exist. However, nothing can be determined with absolute precision.[/quote]While this is true of experimental physics, it is not true of theoretical physics, and its inability to be absolutely determined theoretically indicates that it does not exist even theoretically.

I just argued there is no universal absolute rest frame; only a local absolute rest frame, defined by the local CMB rest frame.

The CMB rest frame is cosmological, like the CMB itself.
And varies from point to point preventing it from being a universal absolute rest frame.

Apr 30, 2016
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Apr 30, 2016
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Apr 30, 2016
Because the variations in the CMB indicate that it has no universal absolute rest frame and cannot.

I do not see your point. The fluctuations in the CMB can indicate temperature fluctuations and/or velocity fluctuations of baryonic matter at the moment it decoupled. Its average would determine the rest frame.
But that average cannot be determined by any measurement we can ever make; we cannot measure local CMB rest frames for remote objects without going there. And we'd have to go *everywhere*. There is no remote way to measure CMB anisotropies that are not gross enough to affect the matter and energy of remote galaxies.

Apr 30, 2016
.... there are no 'local absolute frames of reference', and there are no 'universal absolute frames of reference',.... as this would violate https://en.m.wiki...variance as this would imply some preferred coordinates,.... undermining GTR. [...]

Your statement violates observation. Which do you prefer to violate ?


How so? You could theoretically use the solar system as a frame of reference,.... this does not mean that such a reference frame is absolute which is the sense in which "preferred coordinates" implies that the laws of physics would take on a different form instead of being invariant to changes in reference frame.

Again, I'm not denying that the CBMR is a useful reference frame,.... only that it is "absolute IRF" and that it implies an ontology of space-time.

................

The CMBR is believed to be isotropic and homogeneous, thus the discussion should accept that as a preliminary.

Apr 30, 2016
The CMB rest frame is cosmological, like the CMB itself.
And varies from point to point preventing it from being a universal absolute rest frame.

Explain what you mean.
a) how does a cosmological phenomenon vary form point to point.
As measured in the CMB anisotropies.

b) if it did, how would you know unless you have data from an alien space observatory in the Andromeda system ?
Not needed. The anisotropies in the CMB prove it without the need for remote observatories.

Apr 30, 2016
.... there are no 'local absolute frames of reference', and there are no 'universal absolute frames of reference',.... as this would violate
Noum doesn't get the implications of the CMB frame. No surprise, real observations and real experiments are always where philosophers stop "getting it." See the Sokal Affair.

Your statement violates observation. Which do you prefer to violate ?
Precisely.

Apr 30, 2016
.... there are no 'local absolute frames of reference', and there are no 'universal absolute frames of reference',.... as this would violate general covariance, as this would imply some preferred coordinates,.... undermining GTR.


Noum doesn't get the implications of the CMB frame.


If that were so you would be able to specify how I'm wrong, rather than posting a "subjective characterization" of me.

No surprise, real observations and real experiments are always where philosophers stop "getting it."


I've been referencing mainstream GR in this thread while you have been making philosophical statements about a supposed ontology of space-time. GR de facto represents present understanding,... thus either 1) GR was violated, 2) you have a new theory, or 3) you're speaking philosophically.

None of which I mind, just be clear and admit to one or another.


Apr 30, 2016
I see two possibilities:
1) The CMB only sets a local reference frame. It looks different from different cosmological position and that difference is not explained by a relative speed difference.
2) The CMB sets a cosmological reference frame.
I do not see how option 1) is compatible with the hypothesis that the CMB has a cosmological origin. If 1) is correct then present cosmology is fundamentally flawed. Since you opt for 1) - this without direct observational evidence for either 1) or 2), do you reject present cosmology ?
You are making the unstated assumption that because the CMB has a cosmological origin it is therefore perfectly homogeneous and isotropic. This ignores quantum fluctuations and inflation and is therefore not physical.

Apr 30, 2016
Your statement violates observation. Which do you prefer to violate ?


How so? You could theoretically use the solar system as a frame of reference,.

The CMB is believed to have been emitted by the entire baryonic universe some 100.000 years after the big bang. It sampled the velocity distribution of the baryonic component of the entire universe. Therefore its average velocity coincides with the average velocity of the baryonic universe at that time. Assuming equilibrium with possible other components, say DM, you could even argue that the CMB rest frame is that of the entire universe.

Yes, I understand that. The question was how does my statement concerning reference frames violate observation,.... after all I have pointed out that I am not disputing that the CBMR can be used as a reference frame.


Apr 30, 2016
The CMBR is believed to be isotropic and homogeneous, thus the discussion should accept that as a preliminary.

A minor point but it is _observed_ to be as good as but not entirely isotropic and homogeneous.
Observation trumps belief in my opinion.


I'm trying to help you :). To determined cosmological scales , it is isotropic and homogeneous and so USEFUL as a reference frame,.... but Schneibs previous post is correct, this reference frame does not imply an ontology for space-time .


Apr 30, 2016
I do not make nor do I need such assumptions. At the moment of decoupling the H plasma was not perfectly homogeneous or isotropic. It did determine a frame of reference...
Mutually exclusive. It was or it wasn't. Make up your mind.

Apr 30, 2016
Hi guys. :)

I can't tell you how very good it is to see high quality scientific discourse without past personal animosities and feuds getting in the way. Sincere thanks and kudos to all concerned. Great stuff! I will make my own observations on the discussions so far, in impartial and constructive spirit which I hope no one takes offense at (like they may have done once upon a time)...

CMB as Cosmological reference frame: Phys1 is correct. If big bang is true source of CMB, then the omni-directional pattern/incidence of CMB photons at same speed (lightspeed) represents a globalized averaged out pattern against which can be measured both a 'local/transient' proper speeds relative to it AND ALSO a 'globa/persistent' relative speed relative to it.

Phys1 and Da Schneib both correct, in respective domains of applicability. Local/transient measurements are different from overarching theoretical understanding of CMB involving many measurements over many times/directions.

cont...

Apr 30, 2016
...cont

Consider: If big bang is so, and light speed does not vary, then the omni-directional CMB 'winds' of photons, whose speed is unaffected by anything since initial emission, is the overarching 'neutral background' against which any object can be measured to be moving relative to at its proper speed as calculated from the perceived Doppler effects on the WHOLE SKY in all directions; from which can be deduced A DIRECTION of PROPER MOTION IRRESPECTIVE of QUANTIFICATION precision. In short, we can measure A MOTION with respect to CMB background reference as a GLOBAL frame made by omni-directional pattern of CMB.

Whether a local/transient so calculated is in fact a Global ABSOLUTE motion, is questioned by some. HOWEVER, given the many times over many periods that such motions have been measured, there must be a global status to that motion...unless the CMB omni-directional pattern varies over time....which it CANNOT, due to its unreactive and omni-directional constancy. :)

Apr 30, 2016
@Phys1
That is not mutually exclusive.
Sure it is.

The frame in which the total momentum vanishes is the reference frame.
But you can't prove the momentum vanishes.

Besides the nonhomogeneity is very very small.
Doesn't matter if it's very very small, and furthermore obviously it's big enough to make clusters of galaxies. On our scale that's very very big.

I don't understand why we can't get past this point.
Because the relativity principle shows there is no universal preferred frame of reference, and you're proposing one.

Apr 30, 2016
I don't understand why we can't get past this point.

Because the relativity principle shows there is no universal preferred frame of reference, and you're proposing one.


Exactly correct.

By "preferred" DaSchneib is not saying "we prefer these coordinates because it simplifies our calculations",.... rather he means exactly as I tried to get across above with respect to general covariance,.... that in principle any IRF is just as good as any other in terns of expressing laws of physics.


Apr 30, 2016
.... that the laws of physics are not coordinate-dependent, because coordinates are not "a-priori to nature",.... meaning not "a thing unto itself" that is involved in dynamics. [Schneib will have to substantiate a counter claim to this point in some other way]

The entire reason tensors are used in GR is precisely to extract the observer dependent and arbitrary coordinates so that what is important is not their components but rather their invariant magnitude (referring to 4-vectors).

In essence differential geometry as used in GR allows a coordinate-free representation.

Apr 30, 2016
However if Phys1 is only saying that it is useful as a reference frame and has in fact been used as such, without making any further statements concerning its supposed significance wrt the ontology of space-time,... then he is correct as well...... imo.


Apr 30, 2016
Hi guys. :)
And hi for you too Really-Skippy. How you are Cher? I am doing good or better me, thanks for asking.

I can't tell you how very good it is to see high quality scientific discourse without past personal animosities and feuds getting in the way.
Choot, why you don't try to tell us anyway.

Sincere thanks and kudos to all concerned.
De rien Cher. Glad to make you happy on that.

Great stuff!
See? I knew you could tell us how good it is.

I will make my own observations on the discussions so far, in impartial and constructive spirit which I hope no one takes offense at (like they may have done once upon a time)...

Phys1 is correct.
Well since you say so he might want to double check.

Phys1 and Da Schneib both correct,
I bet you make their day with that. (After they double check.)

Apr 30, 2016
If big bang is so, and light speed does not vary, then the omni-directional CMB 'winds' of photons, whose speed is unaffected by anything since initial emission, is the overarching 'neutral background' against which any object can be measured to be moving relative to at its proper speed as calculated from the perceived Doppler effects the WHOLE SKY in all directions from which can be deduced A DIRECTION of PROPER MOTION IRRESPECTIVE of QUANTIFICATION precision. In short, we can measure A MOTION with respect to CMB background reference as a GLOBAL frame made by omni-directional pattern of CMB.

Whether a local/transient so calculated is in fact a Global ABSOLUTE motion, is questioned by some.HOWEVER, given the many times over many periods that such motions have been measured, there must be a global status to that motion.unless the CMB omni-directional pattern varies over time..which it CANNOT, due to its unreactive and omni-directional constancy.


Nobody could say it better.

Apr 30, 2016
I know the feeling.

Apr 30, 2016
It would be interesting to hear the answer from the author of GR theory to the question how he can define the physical laws, constants of fundamental force interactions which support originaly establishe order in the universe, without absolutes that do not change over time and do not depend on the place in the physical world.

May 01, 2016
I still have the feeling some essential stuff is missing here ...


No doubt !

May 01, 2016
This comment has been removed by a moderator.

May 02, 2016
This comment has been removed by a moderator.

May 03, 2016
Yes but that unique reference frame is only valid at one location. At other locations, the unique reference frame is different.

You're right, it is interesting that a unique reference frame can be defined even for one location; but don't lose track of the fact that it is not a universal reference frame.

May 03, 2016
I think I've understood this. We can use our local CMB to measure the motion of our local group. If we were (say) a billion ly away, we could still measure the motion of the Virgo cluster, but it would be relative to our new CMB, and hence different.
Is that too simplified? Or wrong?

May 03, 2016
@TehDog, seems right to me.

@Phys1, yes, I can back it up, if faraway galaxies were moving relative to the CMB at the rate they're receding relative to us, they would be encountering large amounts of radiation from the blue-shifted CMB in the direction they were moving, and we'd be able to see that being reflected from them. We don't. Thus, their local CMB frame must be receding right along with them, indicating that the CMB frame is only a local frame.

May 03, 2016
Hi Da Schneib. :)
... if faraway galaxies were moving relative to the CMB at the rate they're receding relative to us, they would be encountering large amounts of radiation from the blue-shifted CMB in the direction they were moving, and we'd be able to see that being reflected from them....
I'm not clear on what you mean to say, mate. If the cosmological recession velocities are all radially away from us, then how would we 'see' any blueshifted light from those galaxies? We are behind, not in front, of their recession direction, so only those the 'other side' of those galaxies might 'see' that 'reflected' from them going forward. Also, the pattern of CMB is similar everywhere, that is the Big Bang/Inflation/Expansion hypothesis prediction. So no 'local' variations would be 'visible' from such far distant galaxies locations; and only local proper motions would be variables; and those would be measured as we measure our own location/galaxy motion rel-to CMB pattern. :)

May 03, 2016
@DS
Thanks :)

@Those who know what they're talking about

Ok, I'm assuming isotropy, would there be any difference in the observable energy levels of the CMB if we were much closer to the boundary of our observable universe?
Maybe a dumb question, but I'm not a physicist or astrophysicist :)

Oh wait...
"Thus, their local CMB frame must be receding right along with them, indicating that the CMB frame is only a local frame."

I think that answered my question, I fail at reading...

May 03, 2016
Oops, that didn't answer my question, double fail :)
Would "...their local CMB frame..." have the same energy signature as ours?


May 04, 2016
Oi! Genuine questions deserve answers. (I'll take informed guesses at a pinch... )
My gut instinct says yes. But I'm not sure*, and this annoys me :]
(*for some value of sure)

May 31, 2016
Hi Da Schneib. :)
...

So RealityCheck

Where's the TOE boy???

You wanted a year I gave you a year. Put Up ot shut the fuck up forever!

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