Speed of Light as Universal Speed Limit?

[superstorm]

For the last couple of decades c has been considered as the ultimate speed limit. Until tachyons and gravitons came into the picture.

[Martin]

For the last couple of decades c has been considered as the ultimate speed limit. Until tachyons and gravitons came into the picture.

 

AFAIK there has never been an observation of either a tachyon or a graviton

 

there is no experimental evidence that they exist

 

------------

here is another point:

if gravitons are ever observed, it is widely expected that they will

obey the speed limit----the idea that gravitons will exceed the limit

is a fringe idea

 

(that does not mean it is wrong, the mainstream is not always right, maybe gravitons exist and maybe they can go faster than light, but THEORETICAL reasons would convince most people, i think, that if they exist they must obey the speed limit)

 

anyway so far there is no sign they exist---they just come up in this or that unproven theory---and if they did exist they probably wouldnt break the limit any more than light does

-----------------

here is another point:

tachyons sound good but when they turn up in a theory they are treated as something to get rid of---if it predicts them then somethings wrong with the theory and it needs to be fixed

 

In other words at least to many if not all, if a theory predicts tachyons then that is a problem with the theory

they are generally seen to be fairyland mathematical creatures, not

the daily stuff of physics

--------------------

 

You need to rephrase the question.

Strike out the reference to tachyons and gravitons

and ask a question that has some empirical meaning:

do photons of light ever go faster than c?

 

it is possible that some very high energy gammaray photons do go faster than c and this is going to be tested in the next few years

by a satellite observatory called GLAST

(gamma ray large array space telescope or something like that)

there is a NASA website about GLAST

there are a bunch of mainstream technical journal articles about

the possibility of testing whether very high energy light can go just slightly faster than c

which some new theory suggests might happen for a definite reason

and this can be tested

 

because the most energetic light in the universe comes in these gammaray bursts which come in a pulse, and it will be possible to check with very sensitive instruments like GLAST whether some of the more energetic photons have gotten just a bit out ahead of the others in the pulse

 

so this is a real empirical thing to look for, not "tachyons",

maybe it will be found, maybe not---a good experiment can go either way

 

I should try to find a link about this. GLAST website says they plan to launch in 2007 which is still pretty far away and Bush might cut NASA's

unmanned space instrument budget so GLASt could die on the ground---

lot of uncertainty here

[TheProphet]

Martin: Well we hope that bush soon is out of the game for all sciences sake!

I belive that photons just might go faster than light anyway... but only for short periods to then be canceled out by a slower one! But the sum of it all always remains C! So let's hold a thunmb or two for the GLAST and two down for BUSH...

And for the moment Tachyons is place is still science fiction... but Gravitons seem to come closer to real all the time =)

[J'Dona]

I was under the impression that gravitons, being the predicted but still unobserved force carriers particles for the gravitational force, would have had to travel at the speed of light based on the recent observations of Jupiter when it passed in from of a binary pulsar or some such, allowing them to determine gravity's speed somehow. It was measured at about 1.1c plus or minus 0.2c, which basically makes c the most likely point for it to be. But if gravitons are supposed to be the particles that give mass, I can't imagine how they might travel faster than light, given that their mass would increase to infinity as they approached light speed. I don't know anything about tachyons though, so I can't say anything there.

 

I can't imagine how one photon might be able to travel faster than light just because another is travelling slower though... how would the two rely on each other in that way? Are you talking about some form quantum entanglement between photons, or just spontaneous properties that, in the grans scheme of the universe, cancel out their otherwise bizarre properties somehow? If some theories predict that high energy photons could travel faster than c though, I'd like to know which theory this is and read up on it.

[Tesseract]

There was a young lady named Bright,

 

Whose speed was far faster than light.

 

She went out one day,

 

In a relative way,

 

And returned the previous night!

 

 

-Reginald Buller

[TheProphet]

I was under the impression that gravitons' date=' being the predicted but still unobserved force carriers particles for the gravitational force, would have had to travel at the speed of light based on the recent observations of Jupiter when it passed in from of a binary pulsar or some such, allowing them to determine gravity's speed somehow. It was measured at about 1.1c plus or minus 0.2c, which basically makes c the most likely point for it to be. But if gravitons are supposed to be the particles that give mass, I can't imagine how they might travel faster than light, given that their mass would increase to infinity as they approached light speed. I don't know anything about tachyons though, so I can't say anything there.

 

I can't imagine how one photon might be able to travel faster than light just because another is travelling slower though... how would the two rely on each other in that way? Are you talking about some form quantum entanglement between photons, or just spontaneous properties that, in the grans scheme of the universe, cancel out their otherwise bizarre properties somehow? If some theories predict that high energy photons could travel faster than c though, I'd like to know which theory this is and read up on it. [/quote']

 

Well i agree on the speed of Gravitons.. but that it has mass im not really a go with.. shure can but if it will travel att C it will then act in wave feature! And since we haven't observed it yet ut must interact very wealky with mather and very ghost like too... altough giving very big and observeble notions which we all experince (Gravitation).. Spooky particle i'll like to get my hands on neutrinos act like "Gravitons".. but theorists don't consider em due to mass.. hmmm

 

Well if i'm not completley mistaken Allen Greene states this fact(in his book the elegant universe): That light, or more specific individual light can travel att higher speeds that C but to cancel out att the big picture! When i read it, it was shurely writen as if it was really measured true, but for this im not shure of since he att that moment didn't further empasize it! But indicate that light only travel very short periods with >C<

And as far as im concerned it dosen't need to be high energy photons.. any photon could deviate time for short periods in order to keep C constant! Sounds bizare yes.. but most theories today are

 

And i belive(indeed my belive) that a berkley experiment also point out that C is keept constant so that light never travels in time but only space (sorry Mr.minkowski) that's why we seem to be measuring in experiments the bizare notion that light sees the future... the solution is to keep time constant at Zero.

[Martin]

Hello J'Dona, I will try to find one of the bunch of papers about that----that you asked about---very high energy gamma rays slightly exceeding c.

 

BTW I agree in general with what you said in your post about the best available evidence point to gravity going at same speed as light, namely c.

And also I agree that (whereas tachyons are more SciFi) gravitons are generally predicted by respectable theories-under-development and they merely have not (yet) been observed.

 

As a minor point I think that it is not the graviton but the higgs boson that is supposed to interact with other particles in a way that gives them mass------mass means inertia basically.

 

the Higgs field (THEORETICALLY) would interact with other particles in a way that keeps them moving just the way they are moving, and makes them resist changes of speed and direction

 

so if it doesnt interact with some particle then that particle would have mass = zero

and if it does interact then how strongly it interacts determines how much inertia ( = mass) the particle has

 

it would be wonderful if that theory could be confirmed by actually detecting Higgs particles. but this has not happened so we really should not believe in them too hard.

 

I can't imagine how one photon might be able to travel faster than light just because another is travelling slower though... how would the two rely on each other in that way? Are you talking about some form quantum entanglement between photons' date=' or just spontaneous properties that, in the grans scheme of the universe, cancel out their otherwise bizarre properties somehow? If some theories predict that high energy photons could travel faster than c though, I'd like to know which theory this is and read up on it. [/quote']

 

it may take me a little while to come up with the links, and the articles are all technical as far as I know, so the lay reader just goes for the accessible parts---the introduction at the beginning and the conclusions at the end.

I might be able to find a general-audience paper too but I dont know one off-hand.

 

some names are Lee Smolin, Giovanni Amelino-Camelia, Jose Magueijo, Jurek Kowalski-Glikman, Ted Jacobsson,

some technical terms: Doubly Special Relativity, Quantum Gravity (tests of).

the general idea is that to accomodate quantumness in gravity and also to accomodate things like the cosmological constant and the planck length, it may be necessary to modify the framework of Special Relativity just ever so slightly

 

that is, to bend or deform the space of Special Rel, with effects that occur only noticeably at very high energy or other extreme conditions-----rather like Special Rel modified the space of newtonian physics just slightly with effects that only became significant at very high ("relativistic") speeds

 

and this bending or distorting of the standard framework would allow some photons of light to go slightly faster

but the effect is calculated to be so tiny that one can only notice it (this is incredible!) by looking at a gammaray burst that has traveled something like a billion years!

 

it takes something on the order of a billion years of travel time so that the slighly faster ones can get out ahead of the pulse, enough to notice

 

So GLAST will be able to pick up these brief gammaray bursts and see if there is any sign of some of the photons getting just a bit ahead of the pack.

 

the modification of the speed limit is projected to be extremely small, if it exists

 

sorry I dont have some Quantum Gravity (tests of) papers right handy

but in a day or two i should get back with them.

[J'Dona]

Right, thanks for the explanations. I'd also like to point out a mistake I made which I feel foolish about now... I said that I thought that gravitons had mass, and also travelled at the speed of light in the same breath. No need to point out the error there. :/

 

TheProphet, I'll read up on that part of The Elegant Universe soon. I've got it here at home, just by my desk in fact, and I'd read the first third or so before college concerns forced me to postpone it. Now that college has finished, I'll be able to continue reading it and hopefully find out what I need from that.

 

Also, I believe in the back of The Elegant Universe (p. 392, second paragraph in mine) they give a formula describing any object's motion through spacetime as a result of their velocity in space and velocity in time, which is said to always equal c. As one increases the other decreases, and in the end you have photons which, when travelling at c through space, are not technically travelling through time relative to themselves, which I believe is what you were talking about before. I seriously need to read that again, not the least because my university interview is coming up (again...)

[TheProphet]

Well in the this thread blike puts the math down for the all travels att c and the guy (don't remember his nick) with the funny dancing "alien" as an avatar also states that light travels att c due to avoid decaying! Fun thing was that i came to this conclusion about light without reading Greenes book.. I haven't fully read it yet either(stupid library) Lovely book.. im going to buy it as soon money offers Need more info on String Theory! Since it so hipp now and may describe so much

 

Lorentz transforamtion in the locker again What i was saying is that Due to a constant c Light only travels x,y,z but not t (or most often don't travel t). So in it's frame time is constantly keept 0. That's my point! Darn tired now, but so interesting forum!

[JaKiri]

and the guy (don't remember his nick) with the funny dancing "alien" as an avatar also states that light travels att c[/b'] due to avoid decaying!

 

Well, sort of. I said it was handy.

[TheProphet]

Well, sort of. I said it was handy.

 

Sorry JaKiri; but my English is sort of far from the best So aparden me if i took it a little too far

[ed84c]

There was a young lady named Bright' date='

 

Whose speed was far faster than light.

 

She went out one day,

 

In a relative way,

 

And returned the previous night!

 

 

-Reginald Buller[/quote']

 

 

she would have had infinate energy (e=mc^2g, where g= 1/sqrt1-v^2/c^2) and therefore infinate mass, so, she would have been a rather fat lady called birght!

 

Anyway gravity does appear in the form of waves etc. to obey the rules regarding c, and therfore we prosume if gravitons exist (which I strongly disagree that they do), they follow all rules regarding c

[swansont]

she would have had infinate energy (e=mc^2g' date=' where g= 1/sqrt1-v^2/c^2) and therefore infinate mass, so, she would have been a rather fat lady called birght!

[/quote']

 

Check your math. If you have v>c, g becomes imaginary, not infinite.

[ydoaPs]

Brian Greene wrote the elegant universe, it wasn't Allen Greene.

[Primarygun]

Where the web site is with a lot of complex relativity?

[TheProphet]

Brian Greene wrote the elegant universe, it wasn't Allen Greene.

 

Sorry Folks My mistake!

[Beholder]

Would not the alain aspect experiment suggest that polarized and correlated photons flipped their polarization at a higher than "c" speed? As far as i know, non -locality is faster than "c". Maybe i´m wrong!

[Solaris]

Electric signals can be transmitted at least four times faster than the speed of light using only basic equipment that would be found in virtually any college science department.

 

Scientists have sent light signals at faster-than-light speeds over the distances of a few metres for the last two decades - but only with the aid of complicated, expensive equipment. Now physicists at Middle Tennessee State University have broken that speed limit over distances of nearly 120 metres, using off-the-shelf equipment costing just $500.

 

Jeremy Munday and Bill Robertson made a 120-metre-long cable by alternating six- to eight-metre-long lengths of two different kinds of coaxial cable, each with a different electrical impedance. They hooked this hybrid cable up to two signal generators, one of which broadcast a fast wave, the other a slow one. The waves interfere with each other to produce electric pulses, which can be watched using an oscilloscope.

 

Any pulse, whether electrical, light or sound, can be imagined as a group of tiny intermingled waves. The energy of this "group pulse" rises and falls over space, with a peak in the middle. The different electrical resistances in the hybrid cable cause the waves in the pulse's rear to reflect off each other, accelerating the pulse's peak forward.

 

 

Four billion km/h

 

 

By using the oscilloscope to trace the pulse's strength and speed, the researchers confirmed they sent the signal's peak tunnelling through the cable at more than four billion kilometres per hour.

 

"It really is basement science," Robertson said. The apparatus is so simple that Robertson once assembled the setup from scratch in 40 minutes.

 

While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved, so do not expect super-fast starships or time machines anytime soon.

 

Signals also get weaker and more distorted the faster they go, so in theory no useful information can get transmitted at faster-than-light speeds, though Robertson hopes his students and others can now rigorously and cheaply test those ideas.

 

Physicist Alain Hache at the University of Moncton in Canada adds that it may be possible to use this reflection technique to boost electrical signal speeds in computers and telecommunications grids by more than 50 per cent.

 

Electrical signals usually travel at about two-thirds of light speed in wires. Hache says it may be possible to send unsable electrical signals to near light speed.

 

visithttp://www.newscientist.com/news/news.jsp?id=ns99992796

[Cap'n Refsmmat]

Sweet! Too bad you can't make a starship that uses that...

[Solaris]

Well, it sais not soon. Who knows??? Anyway it is posibile!

[JaKiri]

Well, it sais not soon.

 

That was just a euphemism for 'not at all', I'm afraid.

[AtomicMX]

it would be usefull for computational sciences thought...

[swansont]

While the peak moves faster than light speed, the total energy of the pulse does not. This means Einstein's relativity is preserved

 

That's the relevant part of the article.

 

All they did was reshape the pulse. The effect is no different than the anomalous dispersion experiment that's been discussed eleswhere.

[crAckZ]

http://physicsweb.org/article/news/4/7/8/1

if you travel at 1/2 C in one direction and your friend does the same in the opposite, if you look out the window as you pass will it appear that you are traveling at C?

[Guest HannonRJ]

Light is subject to the classical Doppler Effect, which clearly indicates that Einstein's second postulate is invalid. This conflict with that postulate is one of the reasons why Einstein believed a "transformation" was required in order to "remove" that conflict.