G1.9+0.3: Trigger for Milky Way's youngest supernova identified

March 30, 2016
Credit: X-ray NASA/CXC/CfA/S.Chakraborti et al.

Scientists have used data from NASA's Chandra X-ray Observatory and the NSF's Jansky Very Large Array to determine the likely trigger for the most recent supernova in the Milky Way. They applied a new technique that could have implications for understanding other Type Ia supernovas, a class of stellar explosions that scientists use to determine the expansion rate of the universe.

Astronomers had previously identified G1.9+0.3 as the remnant of the most recent supernova in our galaxy. It is estimated to have occurred about 110 years ago in a dusty region of the galaxy that blocked visible light from reaching Earth.

G1.9+0.3 belongs to the Type Ia category, an important class of exhibiting reliable patterns in their brightness that make them valuable tools for measuring the rate at which the universe is expanding.

"Astronomers use Type Ia supernovas as distance markers across the universe, which helped us discover that its expansion was accelerating," said Sayan Chakraborti, who led the study at Harvard University. "If there are any differences in how these supernovas explode and the amount of light they produce, that could have an impact on our understanding of this expansion."

Most scientists agree that Type Ia supernovas occur when white dwarfs, the dense remnants of Sun-like stars that have run out of fuel, explode. However, there has been a debate over what triggers these white dwarf explosions. Two primary ideas are the accumulation of material onto a white dwarf from a or the violent merger of two white dwarfs.

The new research with archival Chandra and VLA data examines how the expanding supernova remnant G1.0+0.3 interacts with the gas and dust surrounding the explosion. The resulting radio and X-ray emission provide clues as to the cause of the explosion. In particular, an increase in X-ray and radio brightness of the supernova remnant with time, according to theoretical work by Chakraborti's team, is expected only if a white dwarf merger took place.

"We observed that the X-ray and radio brightness increased with time, so the data point strongly to a collision between two as being the trigger for the in G1.9+0.3," said co-author Francesca Childs, also of Harvard.

The result implies that Type Ia supernovas are either all caused by white dwarf collisions, or are caused by a mixture of white dwarf collisions and the mechanism where the white dwarf pulls material from a companion star.

"It is important to identify the trigger mechanism for Type Ia supernovas because if there is more than one cause, then the contribution from each may change over time," said Harvard's Alicia Soderberg, another co-author on the study. This means astronomers might have to recalibrate some of the ways we use them as 'standard candles' in cosmology."

The team also derived a new estimate for the age of the supernova remnant of about 110 years, younger than previous estimates of about 150 years.

More progress on understanding the trigger mechanism should come from studying Type Ia supernovas in nearby galaxies, using the increased sensitivity provided by a recent upgrade to the VLA.

A paper describing these results appeared in the March 1st, 2016 issue of The Astrophysical Journal and is available online.

Explore further: Famous supernova reveals clues about crucial cosmic distance markers

More information: "Young Remnants of Type Ia Supernovae and Their Progenitors: A Study of SNR G1.9+0.3," Sayan Chakraborti, Francesca Childs & Alicia Soderberg, 2016 March 1, Astrophysical Journal iopscience.iop.org/article/10.3847/0004-637X/819/1/37 , Arxiv: arxiv.org/abs/1510.08851

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Bigbangcon
2.5 / 5 (11) Mar 30, 2016
"It is important to identify the trigger mechanism for Type Ia supernovas because if there is more than one cause, then the contribution from each may change over time," said Harvard's Alicia Soderberg, another co-author on the study. This means astronomers might have to recalibrate some of the ways we use them as 'standard candles' in cosmology."

Here goes the "Standard-ness" of our "Standard Candle" and along with it all of the reductionist cosmology of "dark energy", "Big Bang" and other stuff!
Phys1
4.4 / 5 (13) Mar 30, 2016
@BBC
Wishful thinking.
Tektrix
4.3 / 5 (11) Mar 30, 2016
@BBC If you're so incredibly astute, WTF you doing posting your dismissive crap here?
Bigbangcon
2.1 / 5 (7) Mar 30, 2016
@BBC If you're so incredibly astute, WTF you doing posting your dismissive crap here?

Truth always hurts. Sorry, did not realize that it can be so much hurtful for some!
Captain Stumpy
3.9 / 5 (11) Mar 30, 2016
Truth always hurts. Sorry, did not realize that it can be so much hurtful for some!
@bbc
obviously sarcasm and hyperbole are not a part of your retinue...

i can't speak for Tektrix, but i cann add the following, in smaller words for your ease of translation

-if you are so sure and you can prove it with evidence that is reputable and repeatable, you know, like scientific evidence, then why aren't you writing papers and submitting them to peer reviewed journals and collecting your Nobel?

Oh
sorry... didn't mean to bust your bubble with that
Truth always hurts. Sorry, did not realize that it can be so much hurtful for some like you who post pseudoscience
Da Schneib
4.2 / 5 (5) Mar 30, 2016
Excellent. Now we need to look at some more and see if they all have this characteristic X-ray and radio light curve or not. It would be even more helpful if we could determine spectroscopic characteristics that differentiate the two theories. Then we could go back and look at the old spectrograms and see what we see.
Graeme
5 / 5 (2) Mar 31, 2016
Are there any light echos /X-ray echos that could be detected for this supernova?
bschott
2.5 / 5 (8) Mar 31, 2016
@BBC If you're so incredibly astute, WTF you doing posting your dismissive crap here?


It's a comment section under an article that he is commenting about. What do you do? Spray paint your opinion on a construction fence?

Truth always hurts. Sorry, did not realize that it can be so much hurtful for some!


When people think they "know" something, posing logical observations that go against that "knowledge" is damaging to their psyche. This site has posted several articles about the "non standardness" of standard candles in the last few years....it's neat what continued observations of reality do to math based peer reviewed fairy tails....as in expose them as math based peer reviewed fairy tales.
Phys1
3.7 / 5 (6) Mar 31, 2016
@BBC
"Truth" ...
You consider yourself as a reference for the universe, right?
Phys1
4 / 5 (8) Mar 31, 2016
to math based peer reviewed fairy tails....as in expose them as math based peer reviewed fairy tales.

OK so you never passed a math test or a peer review. That does not mean you are less than the next man. It takes every kind of people. I am sure your bullschittt is useful to somebody, although not to me.
Phys1
3.7 / 5 (7) Mar 31, 2016
@BBC

Truth always hurts.

Truth is a double edged sword.
Phys1
3.7 / 5 (6) Mar 31, 2016
@BBC If you're so incredibly astute, WTF you doing posting your dismissive crap here?

Truth always hurts. Sorry, did not realize that it can be so much hurtful for some!

Your posts do not hurt, but they sure do stink.
The truth does not stink.
Manure does.
Use it in the garden not on a science blog.
Captain Stumpy
3.9 / 5 (7) Mar 31, 2016
When people think they "know" something, posing logical observations that go against that "knowledge" is damaging to their psyche
true, take this, for example
Just actual people who have benefited from using the machines and their documented medical results
No, there is no officially documented testing
[so therefore] My evidence is [anecdotal over science]

[but somehow] when the true state of where mainstream science is actually at is shown to the world

[mainstream science] believe what they do, citing the words and interpretations of those whom they believe as evidence that what they believe is correct [except bs forgot all about evidence]
http://phys.org/n...apy.html

My notes and corrections in the brackets to shorten the exchange to relevant points

.

so, has it finally passed the FDA approval?

how is the bet progressing?

still awaiting your replies on that...
Bigbangcon
3 / 5 (2) Mar 31, 2016
Your posts do not hurt, but they sure do stink.
The truth does not stink.
Manure does.
Use it in the garden not on a science blog.

It can also be very good as a fertilizer of the human brain!
Phys1
3.7 / 5 (6) Mar 31, 2016
@BBC
I do appreciate your sense of humour !
Da Schneib
5 / 5 (2) Apr 01, 2016
Are there any light echos /X-ray echos that could be detected for this supernova?
Probably not. It's hidden behind gas and dust clouds; we're only seeing it by X-ray in the first place (Chandra is an orbital X-ray telescope).

Good question though.
Phys1
3.4 / 5 (5) Apr 01, 2016
Are there any light echos /X-ray echos that could be detected for this supernova?
Probably not. It's hidden behind gas and dust clouds; we're only seeing it by X-ray in the first place (Chandra is an orbital X-ray telescope).

Good question though.

X-rays do not echo very well, so it would have to be an optical echo.
bschott
2 / 5 (4) Apr 01, 2016
so, has it finally passed the FDA approval?


Nope, just another 2 lives saved who would otherwise have died if you were involved in any way. Is that your "use" to society? Nothing else seems apparent....

I am sure your bullschittt is useful to somebody, although not to me.


You have no use...but hey, count your blessings. At least your only use isn't to rant on a science forum about adhering to a blatantly broken system.

true, take this, for example....


What followed the above...I am not sure. But it did make as much sense as a usual stumpidiot rant. If you are going to take several portions of posts out of context and attempt to string them together...then add your own..."thoughts", you may want to make sure it all fits together. This is called "language" and is used by humans to communicate with each other.

I'd say try it...but that half brain cell your running on may collapse.
bschott
1.8 / 5 (5) Apr 01, 2016
@ Stumpidiot

For future reference, if you wish to discuss any actual physics relating to an article, or respond to a comment I have made about the physics in an article with your interpretation of the physics, I will be more than happy to chat. If you just wish to continue your rediculous personal evaluations of posters and attempt to enforce your self appointed position of physorg comment regulator by telling others how to comment and what your version of an acceptable answer or post is, I will only answer with an insult, an observation as to why you were an idiot "this time"...and end it with a cheerful "Fuck off idiot".

Cheers, talk you soon no doubt.
Phys1
3.7 / 5 (6) Apr 01, 2016

You have no use...but hey, count your blessings. At least your only use isn't to rant on a science forum about adhering to a blatantly broken system.

You sanctimoniously demand respect for a science forum, respect that you yourself never show, and then to go on to call science "a blatantly broken system".
You are a fool.
bschott
1 / 5 (5) Apr 01, 2016
You sanctimoniously demand respect for a science forum


I did? Seems more likely your comprehension issues are rearing their ugly head again, where have I ever demanded respect for a science forum?

respect that you yourself never show


Not to you, you are unworthy of any.

and then to go on to call science "a blatantly broken system".


Only theoretical science, but i was more referring to "the system" in general. Of course I could obviously have been speaking about your reading comprehension "system" your brain (or lack thereof) attempts to employ.

You are a fool.


"Stars aren't influenced by magnetic fields" - Phys1

Keep on talking idiot king.
Phys1
3.9 / 5 (7) Apr 01, 2016
You sanctimoniously demand respect for a science forum


I did?

Yes you did. Apparently you don't know yourself what you are doing.

respect that you yourself never show


Not to scientists and science in general.

and then to go on to call science "a blatantly broken system".


Only theoretical science, but i was more referring to "the system" in general. Of course I could obviously have been speaking about your reading comprehension "system" your brain (or lack thereof) attempts to employ.

You are a fool.


"Stars aren't influenced by magnetic fields" - Phys1

Keep on talking idiot king.

That is right: the motion of stars is oblivious to the tiny interstellar magnetic field.
Quote me any time, ignoramus.
Captain Stumpy
3.9 / 5 (7) Apr 02, 2016
just another 2 lives saved
@full-of-bs
so you say...

you still haven't learned what scientific evidence means?

if you're so sure it was the machine and nothing else, why hasn't it been FDA approved?
Is that your "use" to society?
my use is pointing out the blatant lies of pseudoscience
you're is promoting pseudoscience

we are diametrically opposed, but i have evidence on my side where you have "anecdote"/repetition
which do you think will eventually win?
If you just wish to continue your rediculous [sic] personal evaluations of posters
so this means you don't like being outed as not being capable of making the argument from evidence...
so you will use ad hominem to point out that you not only *can't* argue from evidence, but have *no refute* other than your ad hominem?

how does that prove your argument at all?

i am trying to help you learn to use evidence for a claim, bub

so, i'm cool with your new tactic

thanks for helping me teach others!
Captain Stumpy
3.9 / 5 (7) Apr 02, 2016
Only theoretical science
@bs
no
sorry

you make these claims a lot when talking about astrophysics, gravity, & satellite fail of detecting gravity... need i post those links?

you also don't know what constitutes evidence for science
you know, like here: http://phys.org/n...apy.html

i was trying to help you see past the pseudoscience and learn how to recognize you were being conned but you lashed out

this is seen elsewhere, but i digress

you routinely denigrate science that doesn't comply with your personal world view, religion, politics or whatever... you label the reasons how you wish. IDC

you justify it with conspiracist ideation as well as things like above in your assessment of the medical device sans actual evidence

you still can't prove, with *any* evidence, that said device has done anything for any person whatsoever, but you say it's true and saved lives?
Enthusiastic Fool
3.9 / 5 (7) Apr 02, 2016
You are a fool.


Somebody call my name? Oh lawdhammercy!

@Stumpman
Thanks for sharing that thread about hard-nosed bschott believing in soft anecdotes about alternative magic magnetic medicine. This was a great April Fools shift.

@Phys1
Does he really believe a force produced by a diffuse interstellar medium that decreases with the cube of the distance has more to do with celestial movement than G produced by high densities of particles that decreases with the square of distance? I wonder how strong a magnetic field would have to be to overcome the inertia of the Sun. Lets not forget that the single charge nature of gravity means it piles up rather well compared to electromagnetism's 2 competing polarities.
Phys1
3.9 / 5 (7) Apr 02, 2016
You are a fool.


Somebody call my name? Oh lawdhammercy!

@Stumpman
Thanks for sharing that thread about hard-nosed bschott believing in soft anecdotes about alternative magic magnetic medicine. This was a great April Fools shift.

@Phys1
Does he really believe a force produced by a diffuse interstellar medium that decreases with the cube of the distance has more to do with celestial movement than G produced by high densities of particles that decreases with the square of distance? I wonder how strong a magnetic field would have to be to overcome the inertia of the Sun. Lets not forget that the single charge nature of gravity means it piles up rather well compared to electromagnetism's 2 competing polarities.

He does apparently. How is this intellectually possible ? It is a mystery of the human brain.
cantdrive85
2 / 5 (4) Apr 02, 2016
a force produced by a diffuse interstellar medium that decreases with the cube of the distance

You're not using the correct physics, the properties of the Birkeland current are a bit more complex than your ignorant understanding.

"This solution reveals the primary effect of the force-free parameter, α, as being a scale factor of radial distance. We show that: 1) both the axial and azimuthal magnetic and current density components cyclically reverse their directions with radial distance from the central axis of the current; 2) the magnetic field extends farther from the central axis within a force-free field than it would if produced by a current in a long straight conductor. The total magnetic field magnitude and current density are shown to vary inversely as the square root of r. For large r, outside the plasma, the azimuthal magnetic
field is shown to vary as 1/r."
http://www.ptep-o...1-13.PDF
Phys1
3.9 / 5 (7) Apr 02, 2016
@cd
So that is why my compass points to the pole of the galaxy.
I thought is it was broken.
It is the huge galactic magnetic field that keeps the sun in check.
The sun is highly electrically charged, hence thunderstorms.
Is that your physics, cd?
Phys1
3.9 / 5 (7) Apr 02, 2016
@bschott
This is the genius with whom I had the following dialogue on Moore's law (yes his knowledge is unlimited).

Phys1: You know better than the CEOs of Samsung, TSMC, Intel, Global Foundries combined.

BullSchitt: Are their eyes connected to their brains?

Phys1: I strongly advise anyone here to put you on ignore or crush you as the scientific and technological insect that you are.

BullSchitt: I strongly advise you to change tampon brands, move out of moms house and find yourself a sexual companion that isn't already part of your physiology. "
RealityCheck
2 / 5 (4) Apr 02, 2016
Hi Phys1. :)

Have you forgotten my pointing out that once the gravity-forward momentum is in balance and a body attains 'free fall' orbital state, a sustained application of an external force/acceleration will SLOWLY affect the body's path through space?

It's not that galactic magnetic forces/patterns 'overwhelm' gravity effect/force on satellite bodies, it's that they ADD another NETT sustained acceleration vector ON TOP of the orbital 'balanced' vectors.

Recall my example re ION DRIVE on Artificial Satellites use a VERY TINY but SUSTAINED THRUST force to slowly redirecting/accelerating the satellite into new 'free falling' orbits or even into higher orbits?

So, if you are going to presume to 'correct' others, you should have regard to ALL the pertinent factors involved; and take scrupulous care to explain which parts are 'incorrect' and which parts may be correct.

Then it's a matter of you/your interlocutors to sort out which stage/factor is being discussed. Cheers. :)
Phys1
3.9 / 5 (7) Apr 02, 2016
@RC
You made these statements before, I remember.
I fail to see your point.
Da Schneib
5 / 5 (7) Apr 02, 2016
@RealityChoke

The whole solar system can't be accelerated by the galactic magnetic field together; the magnetic fields of the Sun and planets are all different, and not in ratio to their masses; some of the planets don't have enough magnetic field to be affected by the galactic magnetic field, so the Sun would be constantly moving in a different direction than they were. This would make an absolute mess of all ephemerides, and unmistakably so.

There simply isn't any evidence at all of acceleration of any object in the solar system by the galactic magnetic field. Period. And we *would* notice it.

And BTW, it's worth mentioning at this juncture that we have now confirmed GRT to a very strong limit: LIGO has detected gravity waves, and not just "some sort of gravity wave" but the unmistakable "ringdown" signature predicted for a black hole merger. Predicted by GRT. No questions, no doubts, no BS.

Stick that up your EU.

Da Schneib
4.4 / 5 (7) Apr 02, 2016
We know the Moon's ephemeris to within a meter or two for five hundred years. Two things are required for that level of accuracy:

1. GRT
2. Laser ranging data for the Moon.

No EU there. And since the Earth's and Moon's magnetic fields are very different, and not consonant with their masses, that laser ranging data would show it. It's not just one shot, it's millions of shots over years.

The EU is a thoroughly debunked fantasy.
RealityCheck
1.8 / 5 (5) Apr 02, 2016
Hi Da Schneib. :)

Re accelerating solar system as a whole, it only takes sun to be so accelerated and planets will follow...as they do now because of earlier system formation dynamics settling into stable orbits even as sun/protosun moving through space. So your objection re that doen't work. As for individual bodies/satellites NOT the sun, their motions are the NETT INSTANTANEOUS resultants of MANY forces/factors acting on them all the time. Sun's gravitational influence; grav influences between planets and on lesser bodies. On top of all Grav influence/factors, there is magnetic field which solar system/galaxy have been confirmed to possess as an overall 'system' magnetic field pattern....modified from time to time by relevant dynamical variations etc. The point was that even small magnetic accelerations BUILD OVER TIME in ADDITION to obvious gravitational ones which determine whether a body is 'captured' or not. It's complex/subtle.

That's all I point out. Cheers. :)
Da Schneib
5 / 5 (5) Apr 02, 2016
Re accelerating solar system as a whole, it only takes sun to be so accelerated and planets will follow
This is the most ignorant thing I have ever seen you say.

You have an imaginary picture of the Solar System as some sort of orrery with sticks connecting the planets to a motor with the Sun on top. The planets are not fixed in position with respect to the Sun; they are under the influence of the Sun's gravity. Moving the Sun causes the gravity at the planets to change; there isn't some mystical stick connecting the planets to the Sun.

Seriously, get a grip dude.
RealityCheck
2 / 5 (6) Apr 02, 2016
Hi Da Scneib. :)
Re accelerating solar system as a whole, it only takes sun to be so accelerated and planets will follow
You have an imaginary picture of the Solar System as some sort of orrery with sticks connecting the planets to a motor with the Sun on top. The planets are not fixed in position with respect to the Sun; they are under the influence of the Sun's gravity. Moving the Sun causes the gravity at the planets to change; there isn't some mystical stick connecting the planets to the Sun.
Not at all. The SUN is the overwhelmingly DOMINANT gravitational mass in our system by FAR.

If the sun SLOWLY affected in its path by subtle persistent galactic magnetic field 'pattern', then the planets have no choice but to follow, with subtle 'transient' gravitational variations in the 'tug' by the sun as the major grav effect. It is KNOWN GR and ORBITAL MECHANICS for our SS.

FYI: PLease understand once and for all, I AM NOT a EU adherent. Ok? Read properly. :)
Da Schneib
5 / 5 (4) Apr 02, 2016
If the sun SLOWLY affected in its path by subtle persistent galactic magnetic field 'pattern', then the planets have no choice but to follow, with subtle 'transient' gravitational variations in the 'tug' by the sun as the major grav effect. It is KNOWN GR and ORBITAL MECHANICS for our SS.
If it's not strong enough to disturb the orbits of the planets for fifty million years then it's not strong enough to change galactic dynamics enough to support denying dark matter.

Now you're just making sxxt up. That's not gonna work either, RealityChoke. There aren't any gaps left. Just give it up.
Da Schneib
5 / 5 (3) Apr 02, 2016
Let me put it another way: you're trying to boil the frog so slowly that it won't notice. You appear to have forgotten you're still trying to boil the frog.
RealityCheck
1.8 / 5 (5) Apr 02, 2016
Hi Da Schneib. :)
If it's not strong enough to disturb the orbits of the planets for fifty million years then it's not strong enough to change galactic dynamics enough to support denying dark matter.
I have never tried to lie or dissemble to you, mate. I use known science and recent discoveries by mainstream, connecting the NEW dots with the old correct dots; discarding old incorrect 'dots'.

The problem is that your bias against me leads you to not read/misread me. So you come back with misapprehensions based on your own misunderstandings/unknowns. If you actually HAD read me correctly/consistently and in context, you would have realized I was speaking from a known science base.

Anyhow, stellar paths always slowly changing in overall galactic dynamics. Didn't you know? There is subtle/not-so subtle changes, depending on which NETT additional force is involved (such as stellar slingshot etc OR subtle/persistent galactic magnetic field accelerations). Ok?

Cheers. :)
Da Schneib
5 / 5 (4) Apr 02, 2016
Oh stop.

"Context."

"Bias."

You've lied twice in the last half hour. And you're doing it again right now.

The mainstream science is GRT, and it's just as effective between the Earth and the Moon as it is between stars at the outer edge of the Andromeda galaxy and its core, and between the Andromeda galaxy and M33. If there were going to be any gravitational anomalies that were big enough to account for dark matter as anything but dark matter, specifically a defect in GRT as you allege, we'd have seen them going on 20 years ago now. So here you are lying yet again.

Just stop.
Da Schneib
5 / 5 (3) Apr 02, 2016
Forget it, RealityChoke. You are boring. You've now descended to ad homs on the other thread, predictably. Lies to insults, your standard trajectory. Just another PO nutjob on ignore.
RealityCheck
1.8 / 5 (5) Apr 02, 2016
Hi Da Schneib. :)

How long will it take you this time to finally admit you got the wrong end of the stick and made accusations of 'lying' which are not borne out by the record in context?

I've nothing against you personally; and I know you have it in you to admit when you're wrong. So I'll ask you to ponder, re-read, understand properly what I posted to humy: regarding the different gravitational vectors/orbiting etc factors which differentiate solar system model from the galactic model using GR principles which produce different Rotation Curves for Solar System than for Spiral Galaxy.

It was naive 'expectations' (based on the S. system modeling/curves) of what galactic rotation curves should be like, that caused initial mis-step of assuming there was an 'anomaly' that needed explanation by some additional 'dark matter' effects; rather than realizing the 'expectations' were incorrect and there was NO 'anomaly' TO explain IF the model appropriately modified for Galaxy. :)
cantdrive85
1 / 5 (4) Apr 03, 2016
You have an imaginary picture of the Solar System as some sort of orrery with sticks connecting the planets to a motor with the Sun on top.

The Sun is directly connected to the Earth via interplanetary Birkeland currents and there is no reason to suggest this connection doesn't exist between the Sun and all it planets. If the Sun and it's plasmasphere are disrupted all the planets will be dragged along for the ride. There is also this asinine assumption about how some here think magnetic fields operate. They've made claims we can't detect the solar magnetic field on Earth or the galactic mag field in the solar system. This is an obvious notion, the Earth's magnetic field shields the solar field, the solar field shields the galactic fields. Even though the fields are shielded in the interiors, the Sun's magnetic field most certainly affects the Earth's. Whoever the moron is that Da-esn't understand this should not be making blanket claims that this is settled and that is wrong.
Phys1
4 / 5 (8) Apr 03, 2016
@cd
Magnetic fields do not shield each other, they addd up.
If the Sun and it's plasmasphere are disrupted all the planets will be dragged along for the ride.

Could you quantify "dragged along for the ride"? Please produce a back of the envelope estimate showing that we are not talking about 10^-99 m/s^2.

The sun must be electrically charged for a magnetic field to affect its motion in the galaxy.
Give a an observationally backed value of the galactic magnetic field and estimate the charge the sun must have in order that its orbit is affected. Provide observational evidence for such a huge charge, like stark effects.
Phys1
4 / 5 (8) Apr 03, 2016
Any student can do the job and disprove your assertions.
Da Schneib
5 / 5 (3) Apr 03, 2016
@cd
Magnetic fields do not shield each other, they add up.
Did cd actually say that he thinks magnetic fields can "shield each other?"

Hey cd, ever heard of vector addition? I'm betting not.
Phys1
3.7 / 5 (6) Apr 03, 2016
@DS
RC is always polite. Let's not change each others nicks.
Besides lying requires knowledge of the truth.
Phys1
3.9 / 5 (7) Apr 03, 2016
@RC
It was naive 'expectations' (based on the S. system modeling/curves) of what galactic rotation curves should be like, that caused initial mis-step of assuming there was an 'anomaly' that needed explanation by some additional 'dark matter' effects; rather than realizing the 'expectations' were incorrect and there was NO 'anomaly' TO explain IF the model appropriately modified for Galaxy. :)

That is exactly what DM does: modify the model appropriately.
As long as no one has shown that DM can not exist and no one comes up with a different "appropriate modification", DM is credible enough.
Phys1
3.9 / 5 (7) Apr 03, 2016
Or rather lying is saying otherwise than what you believe is the truth.
Incorrect or mistaken statements do not meet this requirement.
Enthusiastic Fool
3.7 / 5 (6) Apr 03, 2016
@RC

Hello RC, I gave you a 3 above in a certain post. I believe what you said was at least self consistent and logical in it's own context. In the overall context I think there's probably some misunderstandings. When you have a stable orbit or "free fall" gravity is still in effect. When it's perturbed by an external force it can be fixed via recircularization which is an effect of gravity. If Earth is receding from the sun at 15cm per year due to tidal effects after 4.5 billion years and not the charged particles from solar wind how much is the solar system moved by a much more diffuse field?.
Da Schneib
5 / 5 (2) Apr 03, 2016
@DS
RC is always polite.
No, RC usually maintains a veneer of politeness. And I'm not going to go searching for counter-examples.

Let's not change each others nicks.
OK. All reasonable requests accepted. You may remind me if I forget. I got bad habits elsewhere and struggle with them.

Besides lying requires knowledge of the truth.
Not when two successive sentences contradict one another. Either GRT is correct, or GRT is not correct. One can't have it both ways.
cantdrive85
1 / 5 (3) Apr 03, 2016
@cd
Magnetic fields do not shield each other, they addd up.

Did cd actually say that he thinks magnetic fields can "shield each other?"

Let's attempt to stay on context here. Obviously neither of you are familiar with plasma sheaths or Debye shielding.
Da Schneib
5 / 5 (4) Apr 03, 2016
Let's attempt to stay on context here. Obviously neither of you are familiar with plasma sheaths or Debye shielding.
Both of these effects are localized. And the "screening" is partial at best.
Da Schneib
5 / 5 (3) Apr 03, 2016
When you have a stable orbit or "free fall" gravity is still in effect.
It's important to note that the definition of free fall is local; being in free fall while falling in a gravity field, being in free fall in orbit, and being in free fall in empty open space far from any gravity source cannot be distinguished by any local experiment we can contrive.

To understand this, imagine one is in a closed room with no windows, in any of these three situations. There is no experiment one can perform that will tell one which of these three situations the room is in. Without looking outside (which is non-local), they are indistinguishable.

[contd]
Da Schneib
5 / 5 (3) Apr 03, 2016
[contd]
When it's perturbed by an external force it can be fixed via recircularization which is an effect of gravity.
Actually, no orbit is perfectly circular. All are ellipses. If the Sun were moved by some putative galactic magnetic field, and this motion were toward the current location of a planet that was moved differently by that field, then the consequences to the orbit would be in other parts of the orbit. This is because of the laws of orbital mechanics: west takes you in, in takes you east, east takes you out, out takes you west, north and south bring you back. The strongest effect would be at the opposite end of the orbit. And the laws that govern this are Kepler's Laws.

RC's understanding of orbital mechanics is as defective as hir understanding of gravity physics.

[contd]
Da Schneib
5 / 5 (3) Apr 03, 2016
[contd]
If Earth is receding from the sun at 15cm per year due to tidal effects after 4.5 billion years and not the charged particles from solar wind how much is the solar system moved by a much more diffuse field?.
Not to mention the influence of the solar magnetic field on Earth's geomagnetic field.

Neither of these effects-- solar wind or the interaction of these fields-- is strong enough to have an effect on the ephemerides of the Earth, the Moon (which has a different magnetic field that would also be affected by the Sun's magnetic field, and which would also be subject to a "push" from the solar wind)-- or any other planet. And these ephemerides are calculated using GRT.

Case closed.
cantdrive85
1 / 5 (3) Apr 03, 2016
Both of these effects are localized. And the "screening" is partial at best.

Yep, localized to the objects in question. The Earth and Sun with regards to this conversation. You must understand the scalability of plasma processes, these are merely charged objects immersed in a sea of plasma with many different variables which contribute. Different physics are not required for the description of the action, the foundation of the physics is the same.

And if this "screening" is partial at best, how a diamagnetic cavity in the coma of 67P? And to rehash a ridiculous comment directed toward myself, why doesn't my compass point to the Sun with it's obviously much stronger field?
Da Schneib
5 / 5 (4) Apr 03, 2016
Both of these effects are localized. And the "screening" is partial at best.

Yep, localized to the objects in question. The Earth and Sun with regards to this conversation.
But you're invoking the galactic magnetic field. If it's screened off from the Sun, why would it not be screened off from all stars? And if it's screened off, how can it have any effect on their orbits? Your claim is logically inconsistent.

You must understand the scalability of plasma processes, these are merely charged objects
Neither the Sun nor the Earth is a "charged object." Again, your claim is logically inconsistent.

immersed in a sea of plasma with many different variables which contribute.
What variables? This is an "EU of the gaps" argument.

And if this "screening" is partial at best, how a diamagnetic cavity in the coma of 67P?
Why is "screening" required to explain this? Another "EU of the gaps" argument.

[contd]
cantdrive85
1 / 5 (3) Apr 03, 2016
Actually, no orbit is perfectly circular. All are ellipses.

They're neither circular nor ellipses, they're helical.
This visual annimation shows the the trajectory the Solar System follows as it "orbits" the galaxy.
https://www.youtu...-ooITrws

Da Schneib
5 / 5 (2) Apr 03, 2016
[contd]
And to rehash a ridiculous comment directed toward myself, why doesn't my compass point to the Sun with it's obviously much stronger field?
It's called the "inverse square law," and it's one of the reasons your EU is ridiculous.

Another is the fact that there's anti-charge but no anti-gravity, which means that charges cancel out in nature, but gravity does not.

Let's face it: EU cannot explain dark matter. EM effects are simply not strong enough to do so, because they cancel out. Gravity, because it doesn't cancel out, *is* strong enough to explain dark matter. It's just that simple.
Da Schneib
5 / 5 (3) Apr 03, 2016
Actually, no orbit is perfectly circular. All are ellipses.

They're neither circular nor ellipses, they're helical.
This visual annimation shows the the trajectory the Solar System follows as it "orbits" the galaxy.
https://www.youtu...-ooITrws

That depends on your choice of reference frame, and in the reference frame of the Solar System they are elliptical.

This is moving the goalposts, AKA special pleading, a well-known logical fallacy. You're also claiming that an intertial frame of reference is invalid, which is a violation of SRT. Two fallacies for the price of one.
Da Schneib
5 / 5 (2) Apr 03, 2016
And BTW, if you question whether the Solar System is an inertial reference frame, why do ephemerides based solely on gravity physics give correct answers?
cantdrive85
1 / 5 (3) Apr 03, 2016
Let's face it: EU cannot explain dark matter. EM effects are simply not strong enough to do so, because they cancel out. Gravity, because it doesn't cancel out, *is* strong enough to explain dark matter. It's just that simple.

It's by no means that simple, there is an explanation for "DM". Large scale electric fields;
https://medium.co...1mdw0ftr

And the actual "DM" itself;
http://www.cosmol...hkin.pdf

http://uni-skelet...1_42.pdf
http://uni-skelet...3_64.pdf
http://uni-skelet..._116.pdf
Da Schneib
5 / 5 (3) Apr 03, 2016
I'm not gonna play dueling links with someone who links pseudoscience. Sorry.

Explain it or admit you don't know and are obfuscating by posting links to material you don't actually understand and are therefore incapable of evaluating honestly.

I just explained why large scale electric fields of the power necessary to explain the effects of dark matter cannot exist, and gave two compelling reasons. If you don't have any answer but pseudoscience links you are not competent to evaluate then I will take the point as surrendered.
Protoplasmix
4.8 / 5 (4) Apr 03, 2016
To understand this, imagine one is in a closed room with no windows, in any of these three situations. There is no experiment one can perform that will tell one which of these three situations the room is in.
I imagine I'd curse whoever forgot to put windows in, as I commenced to mounting synchronized atomic clocks, one on each wall, where the windows should've been. Then, for:
Case 1: I'd measure an increasing rate of change in the relative rates of change of ticking of each clock, and for
Case 2: I'd measure uniform, oscillating rates of change (and deduce the number of "room days" per "room year"), and for
Case 3: I'd measure no change in the relative rates of ticking for each clock.

Would that work?
RealityCheck
1.8 / 5 (5) Apr 03, 2016
Hi Phys1. :)
That is exactly what DM does: modify the model appropriately./q]Not at all. The Rot Curve observations were 'naively interpreted' using 'naive' ASSUMPTIONS that GR principles were being applied to the correct context when translating the solar system modeling to disk galaxy context. Hence the incorrect conclusion of an ALLEGED 'anomaly' when gal Rot Curve did not 'fit' the 'expected' curve modeled on solar system orbital model.

I explained subtle point further in other thread:

http://phys.org/n...ong.html

Wherein I pointed out that the ss orbits modeled were EXTERNAL to sun mass/surface; whereas the gal orbits of stars are INTERNAL to disc mass. The ss model 'external orbits' curve IS similar in galaxy model when we look at the orbits WELL BEYOND the gal mass disc EDGE.

So, NO actual 'anomaly'. Hence no 'need' for postulating 'exotic' DM at all. And the rest of motional behavior explained by ORDINARY matter being discovered now. :)
RealityCheck
1.8 / 5 (5) Apr 03, 2016
Hi Phys1. :)
That is exactly what DM does: modify the model appropriately.
Not at all. The Rot Curve observations were 'naively interpreted' using 'naive' ASSUMPTIONS that GR principles were being applied to the correct context when translating the solar system modeling to disk galaxy context. Hence the incorrect conclusion of an ALLEGED 'anomaly' when gal Rot Curve did not 'fit' the 'expected' curve modeled on solar system orbital model.

I explained subtle point further in thread:

http://phys.org/n...ong.html

Wherein I pointed out that the ss orbits modeled were EXTERNAL to sun mass/surface; whereas the gal orbits of stars are INTERNAL to disc mass. The ss model 'external orbits' curve IS similar in galaxy model when we look at the orbits WELL BEYOND the gal mass disc EDGE.

So, NO actual 'anomaly'. Hence no 'need' for postulating 'exotic' DM at all. And the rest of motional behavior explained by ORDINARY matter being discovered now. :)
RealityCheck
2 / 5 (4) Apr 03, 2016
ERRATA: Hi Phys1. Please read the edited/corrected-format post above, and ignore the incorrect-format post before it. Thanks. :)
my2cts
3.9 / 5 (7) Apr 03, 2016
Gravity does not depend on any context. The astrophysicists applied gravity laws correctly and found a discrepancy, hence DM.
I don't see why you believe that gravity would depend on WHERE a mass is.
And the rest of motional behavior explained by ORDINARY matter being discovered now. :)

This is an incorrect interpretation of recent research. I pointed this out several times. No author of the work you so loosely refer to supports your view.
Enthusiastic Fool
3.7 / 5 (6) Apr 03, 2016
@Da Schneib
That depends on your choice of reference frame, and in the reference frame of the Solar System they are elliptical.


Lets not forget that that video he linked is wrong in more ways than one. Phil Plait of "bad astronomy" fame has a write up on Slate about it. In that video the planets are never on opposite sides of the sun out of view of one another. Like you said though, if he wants to call the motion of the planets non-circular because of their motion around the galactic center I say hey more power to him but he should be correct in his understandings of the motions. Why stop there? Dont forget to factor in the Milkyway's movement wrt the local group and then that motion wrt the Virgo Cluster and ultimately the motion of all of Laniakea. It's almost as if movement and velocity are all relative...
Da Schneib
5 / 5 (3) Apr 04, 2016

Case 1: I'd measure an increasing rate of change in the relative rates of change of ticking of each clock, and for
Case 2: I'd measure uniform, oscillating rates of change (and deduce the number of "room days" per "room year"), and for
Case 3: I'd measure no change in the relative rates of ticking for each clock.

Would that work?
No. Where are you gonna get a clock to measure them against? Remember, you can't look outside. And all the clocks inside the room will behave the same (assuming none of them is broken).
Da Schneib
5 / 5 (3) Apr 04, 2016
if he wants to call the motion of the planets non-circular because of their motion around the galactic center I say hey more power to him but he should be correct in his understandings of the motions. Why stop there? Dont forget to factor in the Milkyway's movement wrt the local group and then that motion wrt the Virgo Cluster and ultimately the motion of all of Laniakea. It's almost as if movement and velocity are all relative...
The really interesting thing about this is, if you add those extra motions, you'll still get the same orbital results when you apply the transform back to the Solar System frame even with all the extra motions added.

SRT says all inertial frames are equivalent, meaning they can all be transformed into one another. It's only accelerated frames that have to have something extra added.
Enthusiastic Fool
3.4 / 5 (5) Apr 04, 2016
The really interesting thing about this is, if you add those extra motions, you'll still get the same orbital results when you apply the transform back to the Solar System frame even with all the extra motions added.
SRT says all inertial frames are equivalent, meaning they can all be transformed into one another. It's only accelerated frames that have to have something extra added.


I follow. I just mean if you wanted to zoom way out and have a tail trailing the Earth's movement from the perspective of someone moving outside the super cluster's frame of reference it would probably be pretty intriguing. Because of how relativity boggles the mind its hard not to assume there's a static external reference frame you can use to get the Earth's absolute motion.
RealityCheck
2 / 5 (4) Apr 04, 2016
Hi Phys1/my2cts. :) Please also refer to exchange with Da Schneib in thread:

http://phys.org/n...ong.html

I explained in more detail the subtle aspects which are easily missed if not careful.

Now this:
Gravity does not depend on any context. The astrophysicists applied gravity laws correctly and found a discrepancy, hence DM.
I don't see why you believe that gravity would depend on WHERE a mass is.
They applied laws correctly to derive solar system rotation curve, which were Keplerian, because they described orbits outside the sun, above/away from its surface.

Whereas the Galactic rotation curve OBSERVED was of orbits WITHIN the mass of the disc; hence these are NON-Keplerian orbits/rotation curves IN FACT not in theory.

They necessarily DIFFERENT. Hence the assumption that, since the 'expectations' of Keplerian was not matched in galaxy, then 'exotic' DM 'must' be in play.

But difference IS CORRECT per GR in-DISC orbits, WITHOUT DM. :)
Da Schneib
5 / 5 (3) Apr 04, 2016
RC, you have been utterly owned on that thread.

Here is a list of the things you got wrong:

Yellow curve going up, dotted curve going down; in the picture I posted, this shows that the light curve of the visible part of M33 is inconsistent with GRT.

Dotted curve goes up, which it would never do if astrophysicists were using solar system dynamics; this shows that astrophysicists were using a model consistent with GRT.

You claimed to see "rings" and "gaps" surrounding the nucleus of M33.

You claimed there are "spherical" spiral galaxies.

You claimed there are "non-Keplerian" orbits.

You claimed there is non-inverse square gravity.

You claimed M33 has a "super-massive" black hole.

You claimed there are "spherical" central bulges in spiral galaxies. They are ellipsoids.

You claimed spiral galaxies are flat because they have central bulges.

You claimed there are galactic "orbitals."

You claimed spiral arms are "rings."

I left out your ten insults.
Da Schneib
5 / 5 (3) Apr 04, 2016
The claim that astrophysicists "forgot" Newton's shell theorem and got galactic dynamics wrong is not only proven wrong by the dotted line expected rotation curve for M33, it's also insulting to four generations of astrophysicists.

This is disgusting behavior.

RC, please stop slandering real working scientists.
my2cts
3.7 / 5 (6) Apr 04, 2016

They necessarily DIFFERENT. Hence the assumption that, since the 'expectations' of Keplerian was not matched in galaxy, then 'exotic' DM 'must' be in play.

But difference IS CORRECT per GR in-DISC orbits, WITHOUT DM. :)

Of course the astrophysicists took the observed mass distribution into account.
Are you really claiming they did not? That they made the simplest of all mistakes?
Da Schneib
5 / 5 (2) Apr 04, 2016

They necessarily DIFFERENT. Hence the assumption that, since the 'expectations' of Keplerian was not matched in galaxy, then 'exotic' DM 'must' be in play.

But difference IS CORRECT per GR in-DISC orbits, WITHOUT DM. :)

Of course the astrophysicists took the observed mass distribution into account.
Are you really claiming they did not? That they made the simplest of all mistakes?
Yes. Yes, he is. No question.

He doesn't appear to get what it means that the predicted rotation curve based on the visible matter goes up from the center of M33 to about 10kly out. This shows clearly that they couldn't have made this mistake. So you don't have to thread hop, check this out: https://en.wikipe...on_curve

Look at the first picture. The predicted rotation curve is the dotted curve; the actual observed curve for the visible portion of M33 is the yellow curve.
RealityCheck
1.8 / 5 (5) Apr 04, 2016
Da Schneib's posts above, make it necessary to post mine from the other thread:
The discrepancy between the observed curve and the expected curve based on the visible mass distribution requires explanation, and there are only two explanations possible: 1. GRT is wrong. 2. There is dark matter.
You left out the bleeding obvious THIRD option which I have been patiently pointing out and explaining to you for how long now? That third option: that GRT is CORRECT....BUT the comparison/expectation of curves was NOT done 'apples with apples'; they were applying that CORRECT GRT in NON-Equivalent comparison regions, as I explained (ie, Keplerian compared with NON-Keplerian region of 'orbit' types/speeds profile). If you can 'get' that, then you'll 'get' all I have been explaining to you. Good luck and goodnight, mate.

PS: Please try to take time out to re-read it all; and please stop making 'lists'/assertions based on your own misunderstandings...
Da Schneib
5 / 5 (3) Apr 04, 2016
Reported for spamming.

Meanwhile, I thought you were leaving.

And while we're at it, "non-Keplerian orbit" is pseudoscience, as I told you on the other thread.
RealityCheck
1.8 / 5 (5) Apr 04, 2016
Hi Da Schneib. :)
Reported for spamming.

Meanwhile, I thought you were leaving.

And while we're at it, "non-Keplerian orbit" is pseudoscience, as I told you on the other thread.
So repeating ONE information post across two threads, because your posts in both threads are related, is now "spamming". How convenient/confirmation biased is your definition there?

And I WAS leaving; but I did you the courtesy of holding off leaving in order to answer your posts which required immediate attention since I saw them as I was about to leave. Does having courtesy for another member qualify it as another negative 'item' for your list?

And since you obviously have no clue what I was talking about which is correct science re orbitals graphing/labeling, you should do more of that 'research of your own' on it. You might learn something. I don't lie or dissemble; it's just you don't know what is or is not science/correct in this instance, just as in previous instances. G'night.
Enthusiastic Fool
3.4 / 5 (5) Apr 04, 2016
@RC

When you say galactic rotation curves INSIDE the disk vs OUTSIDE etc etc Non keplerian...blah you remind me of a Clark and Dawes sketch where the front fell off and the ship has been towed "beyond the environment."
https://www.youtu...qxZm_JqM

The Solar System is still "inside" the environment. It's not just the sun's gravity at work here. The planets interact too. If not directly then through their interaction with the Sun. That's how you have orbital resonances. It's all "inside" and it's all Keplerian.

@Da S
Cool I didn't know the Triangulum Galaxy had an intermediate mass BH vs SMBH.


Protoplasmix
4.8 / 5 (4) Apr 04, 2016
Case 1: I'd measure an increasing rate of change in the relative rates of change of ticking of each clock, and for
Case 2: I'd measure uniform, oscillating rates of change (and deduce the number of "room days" per "room year"), and for
Case 3: I'd measure no change in the relative rates of ticking for each clock.

Would that work?

No. Where are you gonna get a clock to measure them against? Remember, you can't look outside. And all the clocks inside the room will behave the same (assuming none of them is broken).
No? You have a problem with gravitational time dilation? You have a problem with general relativity? Wow. Of course it would work – because the clocks are being measured against each other, and no external clock is required, unless you think the laws of physics are somehow different in a windowless room...
Da Schneib
5 / 5 (2) Apr 04, 2016
@Proto,

Some quick questions:
Why would you measure an increasing rate of change in the relative rates of the clock ticks in case 1?
Why would you measure oscillating rates of change in the relative rates of the clocks in case 2?

Remember that both clocks are in the room with you. The essential question is, how would one clock experience a different environment than the other?

Let's start there.
Protoplasmix
5 / 5 (4) Apr 04, 2016
Why would you measure an increasing rate of change in the relative rates of the clock ticks in case 1?
For case 1, the room is in free-fall towards something massive. The side of the room closest to the mass is deeper in a gravitational well which will make that clock tick more slowly. The strength of this gravitational gradient will increase as the distance between the room and the mass decreases.

cont'd >
Protoplasmix
5 / 5 (4) Apr 04, 2016
> cont'd
Why would you measure oscillating rates of change in the relative rates of the clocks in case 2?
Take the simplest example, the room is not spinning. At time t_0 the clock on your left is ticking slower than the one on the right and the one in front is ticking exactly the same as the one behind. Call this "summer." When the room completes a quarter revolution, now time t_1 or "fall," the left and right clocks are ticking at the same rate but the front clock is ticking slower than the clock in back. At time t_3 or "winter" when the room is halfway around in its orbit, the clock on the left is now ticking faster than the one on the right and the front and back are again ticking at the same rate. You can do the math for "spring" and back to "summer" again. The function is obviously sinusoidal.

cont'd >
Protoplasmix
5 / 5 (4) Apr 04, 2016
> cont'd
Remember that both clocks are in the room with you. The essential question is, how would one clock experience a different environment than the other?
In cases 1 & 2 there will always be a gradient to the curvature of spacetime. The clocks are not exactly in free-fall; they're fixed to the walls, held up (or in place) by the room which is in free-fall. There is no relative motion between the clocks but there is a gradient to the force from gravity from one side of the room to the other for cases 1 & 2.
Protoplasmix
5 / 5 (4) Apr 04, 2016
oops, I made a mistake of cardinal proportions there for case 2 above -- "winter" is time t_2 and t_3 would be "spring" ...

Also note, if gravity didn't work that way, it would be awfully hard to explain the observation of comet Shoemaker-Levy 9 as it freely fell into Jupiter ...
Protoplasmix
5 / 5 (4) Apr 04, 2016
Also note, if gravity didn't work that way, it would be awfully hard to explain the observation of comet Shoemaker-Levy 9 as it freely fell into Jupiter ...
qualifier: unless you're an electric universe adherent, in which case it's easily explained by exploding electrostatic discharge of field-aligned Birkland currents. There you have it.
Da Schneib
5 / 5 (3) Apr 04, 2016
Excellent, a very cogent explanation. I actually expected someone who knows more GRT than I do to speak up, but only about the falling case. You surprised me with the orbiting case.

In the falling case, one could use two test masses and measure the space between them; over time, as the room approached the gravity source, they would converge, because the line to the center of gravity of the source for each mass would be at a different angle.

I learned something today. Thanks!
TehDog
5 / 5 (5) Apr 04, 2016
Hmm, I get the sense you're looking "outside the box" with the clocks, which to me, kinda defeats the idea of the thought experiment. Yeah, I'm just quibbling, nice explanation Proto :)
Da Schneib
5 / 5 (3) Apr 04, 2016
Hmm, I get the sense you're looking "outside the box" with the clocks, which to me, kinda defeats the idea of the thought experiment. Yeah, I'm just quibbling, nice explanation Proto :)
The exact item in question here is the Equivalence Principle, which states that in the weak limit, which is often indicated in discussions of relativity by the phrase "local experiment," acceleration is indistinguishable from a gravity field. However, this is not actually true in the case of a point gravity source; this is because a gravity field propagates in 3D space, which means it has a geometry that can be detected by the experiments @Proto suggested with clocks, and the one I suggested with test masses.

[contd]
Da Schneib
5 / 5 (3) Apr 04, 2016
[contd]
One way I like to think about this is to consider, rather than a point source of gravity, a plane source; then, in my falling case the vectors of the test masses would point to the closest point on the plane, rather than to the point source, and their angles would not converge with decreasing distance, and thus the equivalence principle would be exactly true. Because real gravity sources are point sources, it is true only in the weak limit.

One can visualize the weak limit by either considering the gravity field far enough from the point source, or by having the test masses close enough together, so that the equipotential surface of the gravity field within the experiment is so close to a plane that its curvature cannot be measured.

The lesson is, you must understand the limits of the application of the equivalence principle. It applies to an ideal situation, not to the real situations we encounter in the real world.
Protoplasmix
5 / 5 (4) Apr 04, 2016
Small correction to case 2, there's a special case where there would be no oscillation but you would presumably spend all "year" swapping clocks from wall to wall (and corner to corner), trying to figure out why time was consistently passing more slowly on one side of the room than the others – it's the case when there's exactly one "room day" per "room year," like how the moon orbits the Earth.
Da Schneib
5 / 5 (2) Apr 04, 2016
Right, the perfectly circular orbit, tidally locked.
TehDog
5 / 5 (5) Apr 04, 2016
"... However, this is not actually true in the case of a point gravity source; this is because a gravity field propagates in 3D space, which means it has a geometry that can be detected by the experiments @Proto suggested with clocks, and the one I suggested with test masses...

Yeah, I get that and agree, but I've always interpreted the freefalling room as being free of any experimental equipment, including clocks, hence the inability to do any experiment to ...
Hmm, I think I'm treating the "observer" as a point source in my interpretation. Am I wrong?
TehDog
5 / 5 (5) Apr 04, 2016
Meh, second thoughts, not a good question, it's a thought experiment to get folks thinking, it did that nicely :)
Da Schneib
5 / 5 (3) Apr 04, 2016
The real question is, did you learn anything new?

I did, so to me it was a good question.
Protoplasmix
5 / 5 (4) Apr 05, 2016
The page on the EP at Wikipedia mentions that the windowless room needs to be small enough for tidal effects to be negligible, but it's possible nowadays to use optical clocks that have verified gravitational time dilation near the Earth's surface with a height difference between clocks of just 33 centimeters, so that's a pretty small room depending on the gravitational potential being measured. See Optical Clocks and Relativity

@Da Schneib, the test-mass idea is very good – you can also measure gravitational waves that way, e.g., proposed LISA
@TehDog, I finally read your username more slowly, all this time I thought you were ThegoD (kidding)
Protoplasmix
5 / 5 (4) Apr 05, 2016
Interesting to note that gravitational time dilation ( t_s = t_f √[1 – 2GM/rc²] ) is related to the time dilation of special relativity ( t_s = t_f √[1 – v²/c²] ) by the escape velocity from the gravitational well (√[2GM/r] ). Just substitute the escape velocity for v in the special relativity equation and it gives the gravitational time dilation.
G – gravitational constant
M – mass of gravitating object
r – observer's radial coordinate
v – velocity
c – speed of light
t_s – proper time between events A and B for slow-ticking observer in the gravitational well
t_f – coordinate time between events A and B for fast-ticking observer arbitrarily far away
Da Schneib
5 / 5 (3) Apr 05, 2016
@Da Schneib, the test-mass idea is very good – you can also measure gravitational waves that way, e.g., proposed LISA
That's the way the fact that the equivalence principle is only valid in the weak limit was first pounded into my head, and it resonates with the test masses in the Cavendish experiment with me, so it's always in my hip pocket. ;)

I think laser interferometers are pretty much going to beat anything you can do with test masses unless we start using particle beams, and lasers are sooo much easier to handle.

I can't wait until they get LISA up and running. The signal/noise ratio will be so much better in space. Not only that but you can make the baseline a lot longer, and for bonus points you can make a tetrahedron instead of a triangle and pinpoint the source in one shot. :D

Da Schneib
5 / 5 (3) Apr 05, 2016
Interesting to note that gravitational time dilation ( t_s = t_f √[1 – 2GM/rc²] ) is related to the time dilation of special relativity ( t_s = t_f √[1 – v²/c²] ) by the escape velocity from the gravitational well (√[2GM/r] ).
Nice. Thanks! That goes in the permanent file! And it shows the relation between the two theories very clearly.

I learned SRT using "old math," so I recognize √[1 – v²/c²] immediately as τ, the reciprocal of the Lorentz factor, useful in calculating time dilation, foreshortening, and other quantities in SRT. Not surprising it appears in that equation!
Protoplasmix
5 / 5 (4) Apr 05, 2016
I think laser interferometers are pretty much going to beat anything you can do with test masses
"Test mass" is actually how they refer to the LIGO mirrors. Another interesting point, to use LIGO technology to detect a graviton you would apparently need mirrors so massive that they would collapse and form black holes...

Also, I think tau is proper time and usually gamma is used for the Lorentz factor (and alpha for its reciprocal), but I haven't read any older texts.
Da Schneib
5 / 5 (4) Apr 05, 2016
I think laser interferometers are pretty much going to beat anything you can do with test masses
"Test mass" is actually how they refer to the LIGO mirrors.
Another little fact to tuck away. :)

Another interesting point, to use LIGO technology to detect a graviton you would apparently need mirrors so massive that they would collapse and form black holes...
:o
=8O

And unfortunately the laser beam wouldn't reflect from them...

Also, I think tau is proper time and usually gamma is used for the https://en.wikipe...z_factor (and alpha for its reciprocal), but I haven't read any older texts.
In older texts, "tau time" is used in some places for proper time, and "t time" is used, again in some places, for coordinate time. t₀ (or t-sub-r, can't find a subscript r...) is often used for coordinate time and t for proper time in equations in such older texts.
TehDog
5 / 5 (7) Apr 05, 2016
"Test mass" is actually how they refer to the LIGO mirrors"

Here's a photo,
https://www.ligo....0101010a

And here's LISA,
http://sci.esa.in...n-space/

Da Schneib, yep, I learned intelligent discussions can still be had here, which is good :)
RealityCheck
2.3 / 5 (3) Apr 05, 2016
Hi Enthusiastic Fool. :)
The Solar System is still "inside" the environment....It's all "inside" and it's all Keplerian.
Why does it seem so difficult for some to actually read/understand properly what their interlocutors are ACTUALLY saying?

Again: I ALREADY said orbits 'outside' sun ARE Keplerian. That was my point.

I ALSO said orbits 'inside' sun NOT Keplerian (because couter-gravitational effects of 'shells' of material ABOVE an in-sun orbital position 'boost' the orbital speed/path parameters to DIFFERENT paths/speeds which are non-Keplerian).

Get the crucial distinction now? GALAXY 'in-disc' stars are in non-Keplerian situation!

Hence initial ERROR was 'expecting' galaxy non-Keplerian (in-disc) Stellar Rotation Curve would/should 'resemble' outside-sun Keplerian Planetary Rotation Curve.

Hence this 'unexpected mismatch' (long explained by ME as per above) is actually CORRECT according to GR in non-Keplerian DOMAIN.

See? NO 'exotic' DM needed after all. :)
RealityCheck
2.3 / 5 (3) Apr 06, 2016
PS: @ Enthusiastic Fool. :)

Don't confuse 'transient' Solar system Planetary gravitational perturbation 'patterns' by OUTER planets on INNER planets as being akin to 'higher shells' in-sun material's gravitational effects on 'lower shell' orbit in sun/disc mass. The planetary influences you mention are transitory and sporadic and change angles/strength according to relative 'configurations' of the planetary material as these 'sparsely distributed' planets themselves move around their very differently scaled spatial/temporal orbital parameters/resonances etc. The ;shells of material in disc and in sun are more constant average over the whole orbital path of affected stars. Only minor variations due to local conditions are at play INSIDE galaxy disc and INSIDE sun mass. They in no way comparable in 'persistence' and averaged out 'perturbatory consistency' over long time/spatial scales along stellar orbits in-disc. See the subtle differences in that aspect as well? Cheers . :)
Protoplasmix
5 / 5 (4) Apr 06, 2016
Another interesting point, to use LIGO technology to detect a graviton you would apparently need mirrors so massive that they would collapse and form black holes...

:o
=8O

And unfortunately the laser beam wouldn't reflect from them...
It's from Dyson's conjecture that there's no conceivable way to do a practical experiment, at all, in the entire universe, that would allow you to detect a single graviton. There are several ways to think about doing it (like making LIGO sensitive enough to do it), but they all turn out to be impossible for practical reasons. In another example, it turns out that the amount of shielding required for neutrinos needs to be light years thick, and it would also collapse in on itself into a black hole. See "Can Gravitons Be Detected?". If you can understand everything in that paper, you're doing pretty well.
Da Schneib
5 / 5 (3) Apr 06, 2016
Thanks, @Proto, I'll read that pretty soon. Downloaded and saved.

For the lazy:

http://arxiv.org/.../0601043
Graeme
not rated yet Apr 07, 2016
"Are there any light echos /X-ray echos that could be detected for this supernova?"
I was hoping that there may be some infrared or radio waves that might have penetrated the dust. But any way it is likely too long now and reflections would be too far off axis.

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