Study finds single photons cannot exceed the speed of light

Jun 24, 2011 by Lisa Zyga feature
The experimental set-up used to detect the maximum speed of a single photon. Image credit: Shanchao Zhang, et al. ©2011 American Physical Society

(PhysOrg.com) -- The rule that nothing can travel faster than the speed of light, c, is one of the most fundamental laws of nature. But since this speed limit has only been experimentally demonstrated for information carried by large groups of photons, physicists have recently speculated as to whether single photons and the information carried by them may be able to exceed the speed of light. In a new study, physicists have performed the difficult task of producing single photons with controllable waveforms, and have shown that single photons also obey the speed limit c.

The physicists, led by Professor Shengwang Du from The Hong Kong University of Science and Technology in Hong Kong, China, have published their study on the ultimate speed of a single photon in a recent issue of . The results have implications for the maximum speed of information transmission by confirming that single obey causality; that is, an effect cannot occur before its cause.

“The greatest significance of our work is that our experimental results bring closure to the debate on the true speed of information carried by a single photon,” Du told PhysOrg.com. “It deepens our understanding of the particle-wave duality of photons and the nature of quantum mechanics. It provides people a clear picture of photons (since the name was invented by Einstein more than 100 years ago) and corrects some ‘wrong’ and confusing pictures from before.”

With recent advances in technology over the past several years, many groups of scientists have been investigating exactly how fast light can travel. Although previous studies have found that the "group velocity" of light can travel faster than c, the "signal velocity" – the speed at which information travels – cannot. In light of this finding, scientists have wondered whether single photons travel at the group velocity or the signal velocity.

To address this question, Du and his coauthors’ demonstration required not only producing single photons, but separating the optical precursor, which is the wave-like propagation at the front of an optical pulse, from the rest of the photon. Previous experiments based on macroscopic electromagnetic wave propagation (involving lots of photons) have shown that the optical precursor is the fastest part in the propagation of an optical pulse. But this study is the first to experimentally show that optical precursors exist at the single-photon level, and that they are the fastest part of the single-photon wave packet.

In order to separate the optical precursor from the rest of the photon, the scientists generated a pair of photons, and then passed one of the photons through a group of cold rubidium atoms, while using an electro-optic modulator to shape the photon’s waveform. The atoms had an effect called electromagnetically induced transparency (EIT), which enabled the scientists to separate the single-photon precursors from the main wave packet. As the optical precursor and main wave packet traveled through a second group of rubidium atoms, the scientists took measurements on the speed of the two photon components.

The scientists found that the precursor wave front of a single photon always travels at c, like the signal velocity of large groups of photons. The main wave packet of a single photon travels no faster than c in any medium, and can be delayed up to 500 ns in a slow light medium where the group velocity is slower than c.

“In the slow light (with a group velocity slower than c) case, the central part of the main wave packet follows the group velocity,” Du explained. “When the medium density increases (with more atoms), the slow group velocity decreases. In the fast light or superluminal (with a group velocity faster than c or negative group velocity) case, the main wave packet seems to get ‘confused’ and does not follow the group velocity. …We are sure that the main wave packet cannot travel faster than the precursor, which travels at c.”

The results agree with previous studies that have analyzed single photons whose precursor and main wave form have not been separated, which have reported an oscillatory structure. The interference of the precursor and the slightly delayed main waveform can explain this structure.

In addition to bringing some closure to the debate on the true speed of information carried by a single photon, the result that single photons cannot travel faster than the will also likely have practical applications by giving scientists a better understanding of the transmission of quantum information.

“Because the amplitude of the rising front of the optical precursor is lossless in any medium (if the rise time of the edge is infinitely short or zero), optical precursors can be used to carry information for optical communication in a loss or absorptive medium, such as underwater optical communication,” Du said, noting that optical precursors experience some loss in practice.

At the moment, as Du explained, optical precursor communication is limited by current technology, so it is not yet practical. However, he thinks that the technology will improve to make the method competitive with current communication techniques.

“In the future, when the electro-optical technology gets improved such that a step rising time can be as short as <10 femtoseconds and can also be detected by a high-speed photodetector directly, optical precursors will have big applications in optical communication; of course, the single photon precursors can be used for quantum communication.

“One may argue that now we have femtosecond lasers which generate pulses with a length of a few femtoseconds,” he noted. “However, we cannot code information on these pulses and they cannot be directly measured by a photodector with current technology.”

Explore further: 'Dressed' laser aimed at clouds may be key to inducing rain, lightning

More information: Shanchao Zhang, et al. “Optical Precursor of a Single Photon.” Physical Review Letters 106, 243602 (2011). DOI: 10.1103/PhysRevLett.106.243602

4.6 /5 (29 votes)

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mindbound
4.5 / 5 (4) Jun 24, 2011
Interesting, but not exactly surprising or unexpected.
PS3
1.2 / 5 (19) Jun 24, 2011
Entanglement will allow faster speeds once figured out.
El_Nose
3.8 / 5 (14) Jun 24, 2011
@ps3

Entanglement will allow faster speeds once figured out.


that is not true -- it is impossible for even entangled particles to share information faster than the speed of light. This has been shown as well. whta make you think otherwise?

Nothing not even information in any form can travel faster than the speed of light.
Lordjavathe3rd
1.3 / 5 (16) Jun 24, 2011
@El_Nose So speed has nothing to do with the substrait it is in? You do realize that light travels slower in water right?

I always thought it was funny that a photon could pass another photon at the speed of light. It seems you geniuses are always making insightful claims that no human can understand because of the paradoxes.

Point being that you change the space around that which is traveling and you can most certainly travel faster than the speed of light. One example might be to exchange the space from one confined area for another. There are probably other aspects of physical law which would allow for traveling in excess of the speed of light.
NotAsleep
4.7 / 5 (13) Jun 24, 2011
@ Lordjavathe3rd, normally when someone refers to the "speed of light" they refer to the speed of light relative to the medium it's traveling through. Your argument is one of semantics. As we currently understand the laws of physics, no information can travel faster than the speed of light in a vacuum.

PS. Substrait? Like the Substraits of Gibraltar?
Javinator
4.3 / 5 (12) Jun 24, 2011
The fundamental law of nature is that the speed of light in a vacuum cannot be exceeded. Particles can travel faster than the speed of light in a given medium.

See Cherenkov Radiation: http://en.wikiped...adiation
Lordjavathe3rd
1.4 / 5 (9) Jun 24, 2011
We do not understand the laws of physics! btw substrait as in medium.

I don't know whether something can travel faster than the speed of light in a vacuum. I doubt that given our level of understanding physics is sufficient enough to decide that.

For example: Kinetic Energy, a fundamental aspect about moving objects. We say that it's transferred from one massive object to another, but it isn't any form of compression. We also say that it isn't the kinetic energy which causes an object to move in so much as one can manipulate the kinetic energy which causes movement. But that kinetic energy exists only in so much as another object transferred it to it in a classical way, i.e. impacted the object.

Furthermore it is commonly accepted that no internal force causes objects to move, but that objects are never really moving anyway because that stuff is all relative.

Also, we don't know if the above scientific finding is rigorous enough to accept.Was the observer effect taken into account?
NotAsleep
5 / 5 (5) Jun 24, 2011
Scientists generally don't look at anything as "given". Rules are made to be broken and, if you take a look at theory, it's possible to move faster than c (see: tachyon). There's obviously a lot to learn and no one is saying we've stopped looking.

Insofar as your discussion on kinetic energy: don't confuse our macroscopic understanding of kinetic energy with our microscopic understanding. The two are used differently.

Lastly, if by the "observer effect" you mean "relativity" then I'd assume the actual researches took it into account or else it would be a terrible quantum experiment! These articles don't usually delve down to that level of detail

And yes, I know what you meant by substrait... "substrate"
NotAsleep
4.4 / 5 (5) Jun 24, 2011
I just had a funny thought: perhaps there's an advanced civilization out there trying to communicate with others in the universe using something like a tachyon thinking, "there's no way anyone would try to communicate with something slow like radio waves!"

We're definitely not as advanced as we think
Tachyon8491
1 / 5 (4) Jun 24, 2011
There is a fundamental paradox implied by instantaneous phase-state correlation in entanglement as proven by Aspect and GHZ in that this is unquestionably superluminal, and, in communicating state-attribution change, IS informational. We need to more deeply consider hidden component-aspects of "information" and "communication." Take also into account Bohm's Implicate Universe and trans-dimensionally interconnected mutual sensitivity. Although we may memetically agree with the metaphysical axiom that "all is one," we have far from achieved its analogue in pragmatic science - there we are still poking around in the dark with a short stick attempting to detect meaningful solidities... Interestingly, if superlumical communication and superluminal spacetime translation (physically) are impossible, we as a species are forever doomed to being locked within the boundaries of our own solar system, the cradle of our evolution. Surely, a cradle is meant to be evolved beyond, and stepped out of...
Lordjavathe3rd
1 / 5 (7) Jun 24, 2011
Are you telling me that we can manipulate the speed of very small objects with out impact? How can we understand the small and not the large seeing the force is the same. Because kinetic energy is such a fundamental aspect of physics and yet has been treated only superficially, I hold that our understanding of physics is insufficient to support a confident attitude regarding travel speed, as kinetic energy is fundamental to travel speed.

I think I read that Newton and some other great minds of the past thought kinetic energy deserved a thorough examination. Good thing modern scientists did give it a thorough examination and now we understand that there is no internal force which causes objects to move. But that movement is a product of space, only humans are so disillusioned to think otherwise.

In so much as physics doesn't relate to natural law, yeah we understand it completely, just like you said.
S_Bilderback
5 / 5 (1) Jun 24, 2011
http://www.nature...038.html

Older reference to the nature of entanglement
NotAsleep
5 / 5 (2) Jun 24, 2011
@ Tachyon, As an engineer, I work with the understanding that nothing is superluminal and I see no evidence that ANYTHING is "unquestionably superluminal" and I dare not stray into the realm of metaphysics. While I appreciate the deep thought of the last half of your post, I would need more evidence to buy into the first half.

@ Lordjava, for every action there is an equal but opposite reaction, although the reaction can take many forms. I was mostly implying that macroscopic interactions are merely simplified representations of microscopic interactions so a true, albeit sheltered, understand of how things work can only be attained at the microscopic level
NotAsleep
2.3 / 5 (3) Jun 24, 2011
http://www.nature.com/news/2008/080813/full/news.2008.1038.html

Older reference to the nature of entanglement


Unfortunately, this is a poorly written article that tries to imply something that doesn't happen. Read the comments at the bottom of the article for some good insight
Lordjavathe3rd
1 / 5 (4) Jun 24, 2011
I agree. I do think that the scientific community should try and figure out what kinetic energy is; how objects move. It would be pretty awesome to have some kind of inertial propulsion, of course powered by real energy, nothing questionable you understand. :)
NotAsleep
5 / 5 (4) Jun 24, 2011
Inertial propulsion? Like the VASIMR space engine? Look it up, it's pretty awesome.

All engines are inherently inertial. Some are just more efficient than others at given applications. Propeller plane vs. jet engine are fun examples
caeman
1 / 5 (1) Jun 24, 2011
So, if a single photon gets too close to a massive gravitational force such that its path of travel is changed, it doesn't get accelerated even just a smidge faster?
Javinator
5 / 5 (8) Jun 24, 2011
To change the direction of the light, the gravitational force would accelerate the light in the direction of the gravitational force, not in the direction of travel.

The speed of light would remain the same. The velocity would change, though, since the direction has changed.
wiyosaya
1 / 5 (1) Jun 24, 2011
FYI - substrait -> http://dictionary...ubstrait

The intended term really is this -> http://www.refere...ubstrate
NotAsleep
3.6 / 5 (5) Jun 24, 2011
I'm pleading "not quantum physicist" on that question, although my engineering understanding is that the speed of the photon will not change relative to its frame of reference.

I'll also eat my earlier words and say I forgot about the effects of gravity appear to act FASTER than the speed of light. An eye-opening article on gravity:

http://www.gravit...vity.htm

I've believed since high school that once we get a better understanding of what gravity really is, we'll open doors to all sorts of strange discoveries and expand ourselves beyond our current, sheltered universe
iPan
1 / 5 (4) Jun 24, 2011
Food for thought:

Light does not have any speed at all.

Spacetime, at the Planck scale, expands at the "speed" of light, photons (light) are embedded in spacetime and carried by the expansion.

Relative to spacetime, light does not move at all, but spacetime carries the embedded photons along with it at the "speed of light".
Lordjavathe3rd
1 / 5 (7) Jun 24, 2011
To be quite blunt NotAsleep, I think that kinetic energy is an object falling into its self through one part of it being more compressed than the other. I think that because a bullet gains its speed through high pressure behind it and low pressure before it, we can reasonably suspect that the speed of any given object from a travelling baseball to a flying rubber band, is due to the same force only internalized. Physics isn't so complex that it has multiple systems that cause the same behaviour.

From what I've read on wikipedia, I'd say that the scientific community already knows everything I posted. So I wonder why they haven't given the topic more time. We could really use a new propulsion technology, I think we all agree.

Hey wiyosaya! Your an asshole, fyi. Do you know what the catholic church did to plato, you fool. Do you seek to reinforce dogma to the point of stagnating progress? Or perhaps your truely concerned with my poor spelling. I wonder

I'm off topic but still cool.
Foolish1
1.8 / 5 (4) Jun 24, 2011
I've always wondered why it is low energy photons with huge wavelenghts follow their indirect wave-like path through space yet still manage to hold the speed record. Why wouldn't something with very little mass accelerated to some large number of .999999999...'s in a straight line beat the meandering photon?
jscroft
4.5 / 5 (8) Jun 24, 2011
So, if a single photon gets too close to a massive gravitational force such that its path of travel is changed, it doesn't get accelerated even just a smidge faster?


No.

Photons always follow a geodesic course with respect to space-time (see http://en.wikiped...ativity) ). The presence of mass alters the topography of space-time in the vicinity of the mass. The consequence of this to an observer in an inertial frame (i.e. FLAT space-time) is that the path of the photon APPEARS curved.
jscroft
1 / 5 (1) Jun 24, 2011
I've always wondered why it is low energy photons with huge wavelenghts follow their indirect wave-like path through space yet still manage to hold the speed record. Why wouldn't something with very little mass accelerated to some large number of .999999999...'s in a straight line beat the meandering photon?


My dog moves WAY faster than I do, but I can walk the length of a football field before he makes it to the ten-yard-line. Why? Because he meanders. If I took HIS path, he'd beat me every time.
NotAsleep
3.8 / 5 (4) Jun 24, 2011
@ LordJava, quantum physicist I am not but mechanical engineer I am. Your post is poorly written at best. What does the statement "Physics isn't so complex that it has multiple systems that cause the same behaviour" mean? The electromagnetic force can push a magnetic object just as well as an explosion, which is to say there are lots of ways to induce similar phenomenon

@Foolish1, photons all travel at the same speed regardless of wavelength. That's something I've had a hard time grasping and continue to struggle with...
Koen
1 / 5 (5) Jun 24, 2011
Einstein swept under the carpet Dayton Miller' irrefutable experimental proof that the speed of light in vacuum varies (is not constant). Secondly, special relativity assumes the upper speed limit is c for any signal (which is the average speed of TEM waves in vacuum), thus it assumes signals other than TEM waves also have upper speed limit c. Such an assumption cannot be proven experimentally, and they call it physics.
Javinator
5 / 5 (3) Jun 24, 2011
Einstein swept under the carpet Dayton Miller' irrefutable experimental proof that the speed of light in vacuum varies (is not constant).


Citation of a source with an experimental method?

Irrefutable experimental proof is a bold claim. Especially if others have refuted it. You'd think it would be used more by other proponents as evidence for the theory if it were...
Isaacsname
1 / 5 (1) Jun 24, 2011
The " rising front " of the photon, this is akin to a bow shock ?

http://en.wikiped...Bowshock
Tachyon8491
2 / 5 (4) Jun 24, 2011
@ Notasleep:-

Study the Bell inequalities, exchange interactions between eigenstates as in Pauli excllusion principle, then the Alain Aspect experiment and the GHZ-proof for multiple-particle entanglement. Phase-attribute communication taking place in entangled particles (separated even by astronomical distance or unvierse-wide) that take place instantandously, CAN only be considered to be superluminal, even if that does not fit into your present engineering paradigm.
NotAsleep
5 / 5 (2) Jun 24, 2011
@ Isaacsname, sort of... I usually don't like wikipedia but they have a good graphic for group velocities of waves:

http://en.wikiped...velocity
NotAsleep
not rated yet Jun 24, 2011
@ Tachyon, I'm not done reading the literature but I have to quit for the day... I've run out of coffee. Unfortunately, the only think that will get me past my engineering paradigm would be for a scientist to do the research and experimentation for me and lay it out in powerpoint format. After that, I'll make a really neat toy with the results.

Bell Inequalities, while I feel they're an interesting thought experiment and are pretty clearly real, don't come across to me as being superluminal. I'll be back late monday to finish reading up on all the other things you've posted
Isaacsname
5 / 5 (2) Jun 24, 2011
@ Isaacsname, sort of... I usually don't like wikipedia but they have a good graphic for group velocities of waves:

http://en.wikiped...velocity

Ok thank you. I really enjoy learning physics, it seems that we could study for multiple lifetimes and only scratch the surface. I like Wiki because of the hyperlinks, they allow me follow the progressions of things and the relations too. I'm not just fascinated with the science, but the characters and stories about them as well.

..as well as the characters on this website....
pauljpease
5 / 5 (7) Jun 24, 2011
I've always wondered why it is low energy photons with huge wavelenghts follow their indirect wave-like path through space yet still manage to hold the speed record. Why wouldn't something with very little mass accelerated to some large number of .999999999...'s in a straight line beat the meandering photon?


This is a misunderstanding of what is waving. The photon isn't moving up and down, although it is drawn that way on paper. What is moving up and down is the strength of the electric and magnetic fields which are quantities in different units (i.e. different dimensions), not space.

Think about sound waves. In a given medium they travel at the same speed but the wavelength differs. A high pitch and low pitch arrive at the same time even though they have different wavelengths.
antonima
4 / 5 (1) Jun 24, 2011
Point being that you change the space around that which is traveling and you can most certainly travel faster than the speed of light. One example might be to exchange the space from one confined area for another. There are probably other aspects of physical law which would allow for traveling in excess of the speed of light.


@lordjavathe3rd Yeah, some guy proved this, its called the scharnhorst effect. You can cancel vacuum fluctuations between two plates, lowering its refractive index, and this will increase the speed of light by some infinitesimally small amount.
Silverhill
4.8 / 5 (9) Jun 24, 2011
Lordjavathe3rd:
I always thought it was funny that a photon could pass another photon at the speed of light.
Not in the same medium, it can't.

Point being that you change the space around that which is traveling and you can most certainly travel faster than the speed of light.
Perhaps you're referring to the Alcubierre warp drive? (http :// en.wikipedia.org/wiki/Alcubierre_drive)

There are probably other aspects of physical law which would allow for traveling in excess of the speed of light.
"Probably"? What is your estimate of the probability here, and upon what do you base it?

I don't know whether something can travel faster than the speed of light in a vacuum. I doubt that given our level of understanding physics is sufficient enough to decide that.
If relativistic effects were not true (including c as a speed limit), particles in accelerators would have been exceeding c long ago. They don't, because they can't.

continued...
Silverhill
5 / 5 (7) Jun 24, 2011
In so much as physics doesn't relate to natural law,
Natural laws are statements of that which is observed in physics.

I think that kinetic energy is an object falling into its self through one part of it being more compressed than the other.
Electrons, for instance, can have kinetic energy, but they are incompressible.

caeman:
So, if a single photon gets too close to a massive gravitational force such that its path of travel is changed, it doesn't get accelerated even just a smidge faster?
No, it cannot get faster. It gets more energetic, though (if it moves inward toward the source of the gravity) -- its frequency increases.
MorituriMax
4 / 5 (4) Jun 24, 2011
Quick and dirty question. I have always wondered, if information cannot travel faster than the speed of light, how do physical laws throughout the universe stay in sync? In other words if all the physical laws (strong force, weak force, elctromagnetism, etc) are the same everywhere (as far as we know) how do they "know" to work the same all the time anywhere from one end of the universe to the other?

Pardon me if this doesn't make sense, arg, hard to express.
Vendicar_Decarian
0 / 5 (34) Jun 24, 2011
"normally when someone refers to the "speed of light" they refer to the speed of light relative to the medium it's traveling through." - KookaMunga

Clap Trap.

c = c relative to the observer, not relative to space.

Vendicar_Decarian
0.2 / 5 (35) Jun 24, 2011
"how do they "know" to work the same all the time anywhere from one end of the universe to the other? " - MMax

Presumably because everything was in close proximity around 13.2 billion years ago.
Vendicar_Decarian
0 / 5 (34) Jun 24, 2011
"photons all travel at the same speed regardless of wavelength." - NotAsleep

Only if they are traveling in a non-dispersive media. Virtually always the media is dispersive so different frequencies propagate at different speeds, and refract at different angles.
Vendicar_Decarian
0.3 / 5 (36) Jun 24, 2011
"Light does not have any speed at all." - ahem

In the photon's frame of reference this is true. To a photon, the universe is 2 dimensional.

"Relative to spacetime, light does not move at all" - ahem

Meaningless.

How about relative to apple pie?

Vendicar_Decarian
0.1 / 5 (36) Jun 24, 2011
The problem with this "experiment" is of course that photon packets are regularly seen arriving at their destination before d/c. That is, the speed of light is exceeded.

Further, the fundamental assumption behind QED and QCD are that photon speeds are infinite between scattering events, and are reduced to c on average through scattering by vacuum energy.

This immediately implies that above the plank cut off c->infinity, and that what this experiment is measuring is still a bulk, statistical characteristic.
Vendicar_Decarian
0 / 5 (34) Jun 24, 2011
"doesn't get accelerated even just a smidge faster?" - caeman

Nope. c = c as long as you can warp space to make it so.
Deesky
5 / 5 (4) Jun 24, 2011
the fundamental assumption behind QED and QCD are that photon speeds are infinite between scattering events, and are reduced to c on average through scattering by vacuum energy.

This immediately implies that above the plank cut off c->infinity, and that what this experiment is measuring is still a bulk, statistical characteristic

I don't think you can draw real world implications for >c velocities due to QED. QED relies on a mathematical trick called perturbation expansion, giving rise to 'fast' virtual photons. Nature herself knows nothing about perturbation theory. So while QED is hugely successful at describing real world phenomena, you shouldn't get too carried away with assumptions about non-detectable byproducts of convenient mathematical technique.
bluehigh
1 / 5 (3) Jun 25, 2011
information can be deduced faster than light speed.
thingumbobesquire
1 / 5 (1) Jun 25, 2011
Leibniz proved Descartes' notion of force based upon momentum was all wet. Leibniz stood on the shoulders of Cusa, who proved that all in the finite world was necessarily limited in a precisely projective manner. Riemann working in this tradition, developed a proof of shockwaves for sound as it moved beyond the transmissabilty of a medium. Einstein, furthering this method of hypothesis, showed that for light, since there is no speed greater than itself, the mass at the shockwave is resolved, as it were, into energy. This takes us back to Leibniz' F=MA. The problem with looking at clock time and somehow attributing a false idea of transfer of information as a base 2, on off proposition, is that time as understood in human, distinctly noetic terms is relative to the continuing development of the perfection of technology. This is what Cusa developed as the progress of the non-other. The foregoing demonstrates that truthful ideas act forcefully to spur on scientific progress over centuries
Vendicar_Decarian
0 / 5 (34) Jun 25, 2011
"I don't think you can draw real world implications for >c velocities due to QED." - Deesky

You are either going to sum over all possible histories or you aren't. If you aren't then you need to provide an alternate physical explanation as to why the method works. If you are content with summing over all histories then you have to contend with the case where some histories have v>c.

You can try to sum a series where all v<=c to produce v=c, but I don't think you will have much success.
MorituriMax
1 / 5 (1) Jun 25, 2011
Venidicar Decarion,
"how do they "know" to work the same all the time anywhere from one end of the universe to the other? " - MMax

Presumably because everything was in close proximity around 13.2 billion years ago.


Well there weren't any people around 13 billion years ago gathering hard data on prevailing conditions, so that's kind of meaningless as an answer.

So, "presumably" is a not very scientific way of saying everything was a certain way way back then; it doesn't necessarily mean that an expanding universe has any bearing on how physical laws propogate throughout the universe. For all we know, things were very different back then and today conditions are not the same as they were.
TheGhostofOtto1923
2.5 / 5 (8) Jun 25, 2011
information can be deduced faster than light speed.
Your statement is meaningless.
Vendicar_Decarian
0 / 5 (34) Jun 26, 2011
"For all we know, things were very different back then and today conditions are not the same as they were." - Whatever

All measurements conducted back to the observtional edge of the universe indicate no change in the known laws of physics that are at work in any physics lab here on earth.

You may speculate that things were different, but that is just speculation.

Definitude03
not rated yet Jun 26, 2011
Not surprising considering that equilibrium between negative and positive are needed for all EM phenomenon. Makes sense to me that a measurable deviance between the photon direction and that inverse energy deviation of the negative field would transcend into the space beyond the positively affected space as the fields traverse the displaced energies beyond.
toejam
5 / 5 (1) Jun 26, 2011
Totally wrong. Measurements are temporal. The study ignores the wave function. Try again. Time is not a law of nature.
bluehigh
1 / 5 (1) Jun 26, 2011
@Otto - not enough detail perhaps, meaningless no. Perhaps the statement does not fall within the strict confines of the definition of Physics. However, it is demonstrably true that within the framework of logic, the acquisition through deduction and extrapolation of data can provide statistically significant information before the same information can be conveyed at light speed. We can start with petty examples such as the information that the Sun will rise here at 5:49AM tomorrow and we know this not because light is going to carry the information to us (except as a confirmation) but that data exists that allows us to predict the specific future event time. Or perhaps with a high probability deduce that Vendi will call someone a Tard within the next month but thats stretching the logic more than a bit.
Callippo
1 / 5 (5) Jun 26, 2011
In Aether theory 4D space-time is an analogy of 3D water surface with two spatial dimensions and one temporal one. Gravitational waves are analogy of underwater sound waves in such case, they manifest with CMBR noise and it's evident, they're a much faster than the waves of light. Photons of radiowaves would spread with slightly superluminal speed in such model too - whereas the photons of short wavelength light (gamma radiation) will spread slower, than the visible light. In addition, the speed of photon undulates due its passing through density fluctuation of CMBR noise. You can imagine, such a photon materializes with CMBR photons temporarily, which leads into formation of particle-antiparticle pairs, which are indeed moving with superluminal speed. The effect of this temporal materialization is the more pronounced, the higher energetic the light is.
Skeptic_Heretic
5 / 5 (7) Jun 26, 2011
@El_Nose So speed has nothing to do with the substrait it is in? You do realize that light travels slower in water right?
No, that's not accurate.

Let's say you can run at a top speed of 15 miles an hour in the plains.

What speed can you run at in deep forest? 15 miles an hour. Why do you travel more slowly in deep forest? Because you run into things and have to stop and start again. Light travels more slowly through dense mediums because it is absorbed and re-emitted by those mediums.
Johannes414
1 / 5 (5) Jun 26, 2011
The roundtrip speed of light cannot exceed c. However, the one way speed of light can take on any value, including infinity. This one way speed has never been measured and probabaly will never be.
Callippo
2.3 / 5 (3) Jun 26, 2011
This one way speed has never been measured and probably will never be.
If it's not measurable, then it's not testable and of physical relevance. But I don't understand, why the one way speed of light should differ from the two way one. Even from aether model doesn't follow something like this. BYW Some experiments are discussed here, so I'm not even sure with your statement regarding the (im)possibility of one way measurements.
http://en.wikiped...of_light
Johannes414
1 / 5 (3) Jun 26, 2011
Calippo - If you read carefully you will notice they all ended up measuring the two way speed of light. The reason is that we are only able to measure relative speeds, not absolutes. The real speed of light is hidden from us, but still constitutes a physical reality. Thats a rather sobering conclusion for scientists. All we really are capable of is to muddle in our own little puddle.
hush1
1 / 5 (1) Jun 26, 2011
"All we really are capable of is to muddle in our own little puddle." - ohannes

The equation to the above statement:

We-me=One less of you.

:)
A quick fix, till you do better.
Deesky
5 / 5 (2) Jun 26, 2011
I actually agree with Callippo (no, not with the aether crankery bit), that it's a purely philosophical notion to attempt to measure the immeasurable. Should such a one-way measurement be possible, it would throw a wrench into Einsteinian relativity, a theory which has withstood the test of time and increasing sophistication of measurement.

Of course, if something like that did happen, it would no doubt spur another revolution in our understanding of physical law, which would be great, however there seems little prospect for that and the matter remains firmly in the philosophical basket. In the absence of in-principle testability, to say c can take on any value including infinity is sophistry.
Vendicar_Decarian
0 / 5 (34) Jun 26, 2011
"But I don't understand, why the one way speed of light should differ from the two way one." - Callippo

Because - as the idea goes - there is a preferred "stationary" reference frame for space, and the "real" value of (c) depends on motion relative to that frame. On average however, (|c | |c-|)/2 = (c)
Vendicar_Decarian
0 / 5 (34) Jun 26, 2011
"to say c can take on any value including infinity is sophistry." - Deesky

Yet the probability of detecting a photon emitted at (x,t)=(0,0) at position (x,0) is greater than zero in QED and QCD.

Feel free to explain that theoretical truism.

Sanescience
3 / 5 (2) Jun 26, 2011
Missed this first time around, sorry this is late:

http://www.cbc.ca...720.html

"experiment only disproves the general misconception that nothing can move faster than the speed of light.

The scientific statement "nothing with mass can travel faster than the speed of light" is an entirely different belief,"
Vendicar_Decarian
0 / 5 (34) Jun 26, 2011
Beware division by small numbers.
Humpty
1.8 / 5 (9) Jun 27, 2011
Faster than light.... LIGHT has been rammed up at way over light speed.

Sun travels west at 3/4 speed of light - emits photon - relative speed 1.75 x light speed..

Sun with planet and astronomer travels east at 3/4 speed of light - captures photon traveling at 2.5 times light speed.

Study = bullshit.

bluehigh
1 / 5 (3) Jun 27, 2011
"experiment only disproves the general misconception that nothing can move faster than the speed of light.


its not a misconception, its true. anything that has mass (relativistic or otherwise) requires infinite energy for FTL velocity. so only massless entities (ie: NOTHING of substance) can achieve a FTL velocity. Nothing can travel FTL


The scientific statement "nothing with mass can travel faster than the speed of light" is an entirely different belief,"


Nothing has no mass. ipso facto the only entity that can achieve FTL velocity is - you guessed it - nothing.

Only two known ways exist to exceed light speed as a matter of fact. 1. Moving through the light barrier (C) at an infinite acceleration so as to have a velocity of C for a time of (or approaching) zero. (remember only travel at C is excluded not less than or faster than). 2. The entity that has velocity of or greater than C is massless. eg: group delay information.
bluehigh
1 / 5 (1) Jun 27, 2011
or as a matter of simple logic - information being a massless entity (the nothing of substance) is often conveyed within time periods that are less than the time light takes to convey the same said information. Therefore information can and does provably exceed light speed velocity.

Edward de Bono would be so disappointed with the propagation of bad thinking, enshrined it seems within some aspects of science that has allowed outdated ideas and limiting language construction to become enshrined.
hush1
1 / 5 (3) Jun 27, 2011
Ohannes

"Thats a rather sobering conclusion for scientists."

All scientists are still inebriated. Exhilarated by getting as far as they have (or getting away) with a round-trip constant. Unpacking the surprise package is half the fun.

You are a bleak geek.

Far be it from me to spoil everyone's fun by solving the one way conundrum. And turn down the $1 million Millennium Prize as my hero did... - I leave you with his words, lol:

"I've learned how to calculate the voids; along with my colleagues we are getting to know the mechanisms for filling in the social and economic "voids". Voids are everywhere. They can be calculated, and this gives us great opportunities ... I know how to control the Universe. So tell me why should I chase a million?"

Now go sulk some more. :)
hush1
1 / 5 (1) Jun 27, 2011
Perelman. :)
TheGhostofOtto1923
1 / 5 (4) Jun 27, 2011
@Otto - not enough detail perhaps, meaningless no. Perhaps the statement does not fall within the strict confines of the definition of Physics. However, it is demonstrably true that within the framework of logic, the acquisition through deduction and extrapolation of data can provide statistically significant information before the same information can be conveyed at light speed. We can start with petty examples such as the information that the Sun will rise here at 5:49AM tomorrow and we know this not because light is going to carry the information to us (except as a confirmation) but that data exists that allows us to predict the specific future event time. Or perhaps with a high probability deduce that Vendi will call someone a Tard within the next month but thats stretching the logic more than a bit.
The majority of the words you use in this post have nonspecific and thus unscientific meaning. ZB 'petty'.
TheGhostofOtto1923
3 / 5 (8) Jun 27, 2011
The liar johann informs about light...

"20 Everyone who does evil hates the light, and will not come into the light for fear that their deeds will be exposed. 21 But whoever lives by the truth comes into the light, so that it may be seen plainly that what they have done has been done in the sight of God." john3

"3 Send me your light and your faithful care, 
   let them lead me; 
let them bring me to your holy mountain,
   to the place where you dwell." psm43

-Science is only the extended application of our senses and our ability to reason which you believe your god gave us. Why would he do this and then not expect us to use them to figure out how his creations work?

Science is the light of truth which leads us. What you sell is only the darkness of ignorance and deceit. Peddle your religionist lies somewhere else.
TheGhostofOtto1923
3.2 / 5 (9) Jun 27, 2011
All we know now are some shadows. That is why people come up with miscalculations like bb or evolution.
Johann the liar cites obsolete studies and posts incomplete info to reinforce his religionist lies. Which is why people who believe what he says know only shadows. People like johann think lying for Jesus is a greater truth.
TheGhostofOtto1923
1 / 5 (4) Jun 27, 2011
Blessed are ye, when men shall revile you, and persecute you, and shall say all manner of evil against you falsely...
Yah Im sure satan says this all the time (if he existed which he doesnt). Youre still a liar in anybodys judgement. This has been proven.

"Proverbs 19:9
A false witness will not go unpunished, and he who breathes out lies will perish.

http://www.openbi...ics/liar

Repent johann of the lying god, who is an atheist in all but one case, according to very specific guidelines.
Skeptic_Heretic
4 / 5 (4) Jun 28, 2011
The roundtrip speed of light cannot exceed c. However, the one way speed of light can take on any value, including infinity. This one way speed has never been measured and probabaly will never be.

No, this is ridiculous, and your further commentary show you to also be ridiculous.
Johannes414
1 / 5 (2) Jun 28, 2011
"No, this is ridiculous"

Then you are calling Einstein ridiculous. He assumed the one way speed of light to be c, but admitted it was just an assumption.

The reason is that to measure the one way speed of light we first must assume its value to be able to synchronize clocks -a contradiction. In fact the one way speed of light theoretically can take on any value between 1/2c and infinity.

The round trip speed of light however cannot exceed c, as many experiments have shown.
hush1
1 / 5 (1) Jun 28, 2011
O'hannes:
Enlighted yourself.

Simply read the German Wikipedia version:
http://de.wikiped...ndigkeit

and the English version:
http://en.wikiped...of_light

...and you will see what you are missing are the 100 words which are not in the English version.

Then report back to us.
Vendicar_Decarian
0 / 5 (34) Jun 29, 2011
"we first must assume its value to be able to synchronize clocks" - Johann....

We observe that well made clocks stay synchronized when in close proximity and when they in the same stationary reference frame.

The presumption is that if moved slowly from point a to b the deviation in synchronization is small and can be made as small as necessary by moving the clocks as slowly as required.

So far, no deviation from this expected behavior has been noticed.

Johannes414
1 / 5 (2) Jun 29, 2011
"Denn obwohl Einweg-Messungen mit Licht bereits durchgeführt worden sind, ist es prinzipiell unmöglich, daraus unzweideutig die Einweg-Lichtgeschwindigkeit bzw. deren Isotropie zu bestimmen, da dies nicht unabhängig von einer Konvention möglich ist, wie die Uhren an der Quelle und beim Empfänger zu synchronisieren sind"

Exactly my point - one way speed cannot be measured without assuming its value to synchronize clocks. Science really operates "in darkness", knowing only the shadow, the round trip speed. Its like a traveller saying: I will be back in a year from now but I will not be able to tell you where I will be in between.
hush1
1 / 5 (1) Jul 01, 2011
"...da dies nicht unabhängig von einer Konvention möglich ist..."

Convention, for sake of convenience, prevents a solution.
There is no need to abandon successful convention, until convention hampers the scientific endeavor or progress.

And when the time comes, this convention will become obsolete, superseded and abandoned. So until we can ascertain an isotropy independent from the convention presently agreed upon for light, our two-way convention for a constant speed of light is by no means a disservice to any branch of science.

I can assure you when convention for the speed of light changes, it will not be from the words of the bible.

"This one way speed has never been measured and probabaly will never be." - O'hannes
No one shares your fatalism.
barakn
5 / 5 (3) Jul 02, 2011
"to say c can take on any value including infinity is sophistry." - Deesky

Yet the probability of detecting a photon emitted at (x,t)=(0,0) at position (x,0) is greater than zero in QED and QCD.

Feel free to explain that theoretical truism.

This occurs because you can't measure both x and t to arbitrary precision. This is just Heisenberg wearing another cloak.
Caliban
4 / 5 (4) Jul 02, 2011
Matt5:11 Blessed are ye, when men shall revile you, and persecute you, and shall say all manner of evil against you falsely, for my sake.

I must say thanks be to the Lord that in His wisdom He even uses the atheists to fulfill His marvellous truth!

John8:21 Then said Jesus again unto them, I go my way, and ye shall seek me, and shall die in your sins: whither I go, ye cannot come.


That's some funny stuff, there, J. Applying the Universal to the specific case, and then citing it as proof of some Eternal, Invariant Truth.

The only Truth revealed by that nonsense is the Truth of Human Behavior. Substitute any other Duality , and the sense remains the same: conservative/liberal, moral/amoral, educated/ignorant, science/faith et c., et c..

Not proof of god- just proof that the graybeards that developed the concept understood human behavior quite well, and were adept at manipulating it to control it for THEIR OWN ends.

Nothing Divine about that.

Caliban
2.3 / 5 (3) Jul 02, 2011
I don't see any problem -in principle- with saying that a photon cannot exceed the speed of light. After all, the two define each other.

At the same time, that doesn't preclude some other energy, or even some other particle, from exceeding that velocity.

Admittedly, I don't possess the knowledge of mathematics or physics of many of you here, but that doesn't prevent me from understanding that much about the universe is unexplained, and that the simple fact of the discontinuity between the universe at the quantum level and at the gross scale leaves a lot of room for possibility.

The fact that the energy level in the primordial universe caused it to expand further than the visible limits that bound our observations of it, is, as a first principle, a pretty good argument for the existence of energy/material capaple of FTL propagation.

Or so it seems to me.

Have at it, everyone!

eachus
not rated yet Jul 02, 2011
I'm surprised that the work of Gunter Nimtz hasn't come up here: http://en.wikiped...er_Nimtz It would be nice to combine the experiments, and see what happens when the "single-photon precursors" encounter Nimtz's prisms.

My belief is that the superluminal propagation is not of a photon, but of an evanescent particle, which could be a tachyon, since we cannot measure its mass or momentum. But experiment trumps belief every time, so I hope someone does the experiment, then measures the recoil, if any, of the prisms.
PS3
1 / 5 (1) Jul 03, 2011
@ps3

Entanglement will allow faster speeds once figured out.


that is not true -- it is impossible for even entangled particles to share information faster than the speed of light. This has been shown as well. whta make you think otherwise?

Nothing not even information in any form can travel faster than the speed of light.

Give it time and I'm sure we can figure a way to use it for information. Here is one theory- h ttp://bit.ly/iXHIjI
Ulaanbatar
2 / 5 (4) Jul 03, 2011
Spacetime should be the simplest thing in nature, not some very complicated structure. Simplest is ideal gas and my ideal gas composed of the structureless speedy tachyons having velocity of 8.10^88C (C=Velocity of light in vacuum) leads to the experimental data, to the quantum mechanics, and to the SR and GR i.e. to the today's fundamental mainstream (NOT ultimate) theories.

Only tachyons (no matter whether bound in particles or free in spacetime) having, as a whole, eternal constant MEAN energy lead to the BASIC conservation law i.e. to the conservation law of energy. It leads also to the Principle of Relativity.

The tachyons lead to global nonlocality (Bohr wins with Einstein) and reality (Einstein wins with Bohr) of the Universe.

Any future development must involve changing something which people have never challenged up to the present, and which will not be shown up by an axiomatic formulation- P.A.M. Dirac.
Skultch
not rated yet Jul 03, 2011
The roundtrip speed of light cannot exceed c. However, the one way speed of light can take on any value, including infinity. This one way speed has never been measured and probabaly will never be.


Maybe I don't understand the 1-way/2-way thing, but isn't it true that calculating the sum of all histories requires an ad hoc removing of infinities? Isn't it true that this trick is still required in basice QM math? Wan't Feynman uncomfortable with this, but still thought it 'true' and necessary?
david534
not rated yet Jul 18, 2011
@Javinator It is impossible for light to travel (phase velocity) as fast as c in any physical medium. That includes Cerenkov radiation, a nonlinear "shock-wave" phenomenon that accelerates light beyond its normal speed in its medium. I have edited the Wikipedia article to make this clear.
david534
2.3 / 5 (3) Jul 18, 2011
It is remarkable that people want to believe "forbidden" things, including the idea that light (or information) can travel faster than c, that perpetual motion or energy from nowhere is possible, and that the configuration of the stars and planets can somehow help to create our personality. I blame the state of our education. Instead of exciting us with the truths of science, our ignorance leaves us open to imagining than anything is possible. It isn't. But the range of possibilities is still far grander than our daily lives typically reveal. An inspiring teacher is a rare and wonderful thing, which can teach us the amazing yet true and achievable possibilities in science and in life.
Callippo
3 / 5 (2) Jul 18, 2011
including the idea that light (or information) can travel faster than c
The speed limit of light is not limit for information exchange. Contemporary physics enables to exchange information with superluminal speed, just in less or more indeterministic way (for example during repetitive attempts and/or without actually knowing, who is your partner in communication). It's dual situation to so-called weak measurements in quantum physics, which are seemingly breaking the uncertainty principle.
Javinator
not rated yet Jul 19, 2011
@Javinator It is impossible for light to travel (phase velocity) as fast as c in any physical medium. That includes Cerenkov radiation, a nonlinear "shock-wave" phenomenon that accelerates light beyond its normal speed in its medium. I have edited the Wikipedia article to make this clear.


I said:

The fundamental law of nature is that the speed of light in a vacuum cannot be exceeded. Particles can travel faster than the speed of light in a given medium.


I never said that light traveled faster than c in a medium. I never said anything traveled faster than c.

I said that particles can travel faster than the phase velocity of light and used Cerenkov radiation as an example. You're taking what I said incorrectly.

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