# Can something move faster than light?

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### Poll: Can something move faster than light? (1 member(s) have cast votes)

#### Can something move faster than light?

Percentage of vote: 58.62%

Percentage of vote: 27.59%

3. I don't know (20 votes [13.79%])

Percentage of vote: 13.79%

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### #307 von Faulkenstein

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Posted 13 June 2007 - 01:27 PM

I did find a website that discusses this idea of galaxies moving at FTL--

"Apparent Superluminal Velocity of Galaxies

A distant object can appear to travel faster than the speed of light across our line of sight, provided that it has some component of motion towards us as well as perpendicular to our line of sight. Say that on January 1st you make a position measurement of galaxy X. One month later, you measure it again. Assuming you know its distance from us by some independent measurement, you derive its linear speed, and conclude that it is moving faster than the speed of light.

What have you forgotten? Let's say that on January 1st, the object is Dkm from us, and that between January 1st and February 1st, the object (which is actually moving at 45 degrees to the line of sight) has moved dkm closer to us. You have assumed that the light you measured on January 1st and February 1st were emitted exactly one month apart. Not so. The first light beam had further to travel, and was actually emitted (1 + d/c) months before the second measurement, if we measure c in km/month. The object has travelled the given angular distance in more time than you thought. Indeed, we can calculate that if its real velocity is v, then its apparent velocity in this case is v/[sqrt(2)-(v/c)] which could be higher than twice the speed of light without v being greater than c. For galaxies moving at more acute angles to the line of sight the apparent velocity can be much higher. Similarly, if the object is moving away from us, the apparent angular velocity will be too slow, if you do not correct for this effect, which becomes significant when the object is moving along a line close to our line of sight.

The effect has been observed in the radio emissions from jets of quasars which are thought to travel close to the speed of light in a direction near to our line of sight."

from--
I can't give this webpage.

### #308 von Faulkenstein

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Posted 13 June 2007 - 01:57 PM

"Although the theory of special relativity forbids objects to have a relative velocity greater than light speed, and general relativity reduces to special relativity in a local sense (in small regions of spacetime where curvature is negligible), general relativity does allow the space between distant objects to expand in such a way that they have a "recession velocity" which exceeds the speed of light, and it is thought that galaxies which are at a distance of more than about 14 billion light years from us today have a recession velocity which is faster than light."
I can't give the webpage, just do a goggle for FTL Information from Ansers.com.
Does it then seem that spacetime or space can have a velocity greater than light "c" but the galaxies in this area of space are not traveling greater than "c" but are being carried by this space not through it?
Regards, Doc

### #309 EWright

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Posted 10 July 2007 - 08:55 PM

"Although the theory of special relativity forbids objects to have a relative velocity greater than light speed, and general relativity reduces to special relativity in a local sense (in small regions of spacetime where curvature is negligible), general relativity does allow the space between distant objects to expand in such a way that they have a "recession velocity" which exceeds the speed of light, and it is thought that galaxies which are at a distance of more than about 14 billion light years from us today have a recession velocity which is faster than light."
I can't give the webpage, just do a goggle for FTL Information from Ansers.com.
Does it then seem that spacetime or space can have a velocity greater than light "c" but the galaxies in this area of space are not traveling greater than "c" but are being carried by this space not through it?
Regards, Doc

This is because space itself is allowed to expand at speeds greater than c. But objects cannot travel faster than c through space according to Relativity.

### #310 Farsight

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Posted 26 July 2007 - 03:33 AM

I consider it a matter of formal theoretical definition that the rest mass of a photon is zero. Because, as Qfwfq notes, photons are theoretically forbidden from appearing at rest in any inertial frame, this zero rest mass is not a physically realizable quality. At their theoretically required speed of c, photons have measurable momentum. In principle, then, they can be considered to have a finite relativistic mass at speed c, with all the effects that implies, though measuring effects more subtle than the pressure due to their momentum is difficult with current experimental technology.

IMHO it's astonishingly simple when you appreciate what's going on. Look at pair production and annihilation. When the photon is "at rest", it isn't a photon any more.

### #311 Guest_Lambus_*

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Posted 27 July 2007 - 07:22 AM

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### #312 Little Bang

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Posted 27 July 2007 - 09:24 AM

if you place two dots on the surface of a balloon and start blowing it up to infinity, at some point in it's expansion those two dots will be separating faster than C and yet nothing has ever exceded C. That presents an apparent paradoxe. To an observer the dots appear to be separating faster than C, but that won't happen because the other dot will red shift out of our observable universe long before it reaches C. BTW the graviton is still a hypothetical particle?

### #313 CraigD

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Posted 27 July 2007 - 05:05 PM

if you place two dots on the surface of a balloon and start blowing it up to infinity, at some point in it's expansion those two dots will be separating faster than C

Little Bang, you appear to be suggesting that the distance between 2 point on the surface of a spherical balloon $D$ being inflated by a constant volume per unit time $\Delta V$ will increase at a greater rate as the balloon becomes bigger. This is not true. The increase in distance between the 2 points for a given unit time is $\Delta D = k ( (V + \Delta V)^{\frac13} - V^{\frac13} )$, where $V$ is the volume of the balloon, and $k$ is a constant.

As the balloon grows bigger, the rate at which the dots move apart grows slower.

### #314 Little Bang

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Posted 27 July 2007 - 07:15 PM

You are correct Craig, I was talking about accelerated expansion as the universe appears to be doing.

### #315 Guest_Lambus_*

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Posted 28 July 2007 - 02:52 AM

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### #316 Little Bang

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Posted 28 July 2007 - 09:07 AM

Since the original question used " Can something " then I would say that some things could have an appearent velocity greater than C but nothing with mass.

### #317 CraigD

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Posted 28 July 2007 - 10:20 AM

If space-time fabric can expand faster than luminous velocity, then why could not a graviton traversing such a hyper-luminous expansion also expand faster than luminous velocity, and hence travel faster than luminous velocity.

Yes. The same is true of a photon (light), or an ensemble of massive particles, such as a rock. The empirical theory of cosmic inflation (empirical, as inflation is required to explain observations, but not the consequence of a well-understood or accepted fundamental physical mechanism) suggest that, at some moments in the history of the universe, nearly all objects had “superluminal” relative velocities, and that at present, many photons do.

As used above, the term “superluminal”, and synonyms like “FTL”, “hyper-luminous”, etc., are problematical. Their most intuitive meaning – traveling faster than a light signal – is inaccurate, as light signals in expanding space are also superluminal.

Consideration of the graviton boson is also problematical, as its existence remains hypothetical, not a integrated and verified part of the standard model of particle physics its hypothesized to extend. Experimentally detecting a single graviton is tremendously difficult, as the force it carries is tiny (about $10^{-25}$ of the next weakest bosons, the W and Z) compared to the other fundamental forces.

Currently, the most promising experiments, several gravitational wave detectors, fall far short of the capability of detecting individual gravitons, but should be able to place limits on the range of possible speeds of the graviton.

However, the graviton is not composed of electromagnetic flux, therefore the graviton flux interaction with space-time must be much faster.

I think this assertion confuses the formalism of particle physics (of which the graviton and photon are terms) and classical electromagnetism (of which “electromagnetic flux” is a term). Particle Physics is a more fundamental family of theories that attempt to explain the empirical laws of electromagnetism. It’s fundamental particles are not subject to the fields of electromagnetism – they are the reason for them.

As noted above, the existence of gravitons is unconfirmed. However, most models of them hypothesize that they are either massless with speed in a vacuum of exactly c, or have a very small mass, and a speed slightly less than c. I know of no formal description of the graviton that predicts it having a speed greater than c.

As an amateur science enthusiast, I’m somewhat frustrated that the most serious and well-funded experimental gravity research seeks, ambitiously, not only to determine the speed of propagation of changes in gravity, but to confirm various theoretical predictions of General Relativity concerning the spatial geometric effects of gravity and actual power (energy loss) of sources of gravitational waves (see the previous link for more discussion). My heavy-handed, simplistic approach to science makes me long for a simple experiment to measure only the speed of propagation of a change in gravity, such as the following:
• Make a machine consisting of a ring (a torus) of a dense ordinary material with a mechanical structure that allows its circumference to be varied
• Place it in gravitationally flat-ish location in space (eg: an Earth-Sun Lagrangian point)
• Place a small test mass in orbit around it at a sufficient distance that the speed-of-light travel time between test mass and ring can be reliably measured
• Change the circumference (and thus the gravitational attraction between the ring and test mass)
• Observe the change in the test mass’s orbit – most importantly, when it deviates measurably from its original orbit.
I’ve not worked out even approximate details for such an experiment, but will in the next few days. I wonder if they’ll show such an experiment feasible? (technically, not politically or financially)

### #318 CraigD

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Posted 28 July 2007 - 01:13 PM

I find a few disagreements between the supporting references and the claims in Lambus’s list of statements. Addressing each in turn:

A graviton is a hypothetical particle with zero mass. (wiki)

Although the most common description of the graviton hypothesizes a zero rest mass and a speed in vacuum of exactly c, (the graviton is identical to the photon, except than its spin is 2, not 1) others hypothesize a non-zero rest mass and a speed less than c. (see wikipedia articles “list of particles, Bosons (integer spin)” and “Graviton”)

A Tachyon is any hypothetical particle with zero mass that travels at superluminal velocity. (wiki)

Nowhere in the wikipedia article “Tachyon” do I find it stated that a Tachyon has zero mass. Rather, the article shows a derivation of the mass of a tachyon having a non-zero imaginary (having a term of $i=\sqrt{-1}$) value.

A hyperluminal or superluminal Graviton is a Tachyon.

That such a particle exists is nowhere supported in the provided references, and doesn’t appear to me to follow from the preceding definitions

A Photon is a elementary particle with zero [rest] mass (wiki)

Correct.

A hyperluminal or superluminal photon with zero mass is a Tachyon.

At with the preceding proposed “superluminal Graviton”, the existence of a photon with velocity greater than c is nowhere supported, and doesn’t appear to follow from the preceding definitions.

A superluminal photon tunneling through a quantum tunnel is a Tachyon.

Again, none of the provided references support the existence of a “superluminal photon”

Also, I sense some confusion in the use of the phrase “quantum tunnel”. Other than a reference to a joking reference in the Simpson’s episode “Future-Drama and other science fiction references, “tunnel” is used only as a verb, not a noun, in quantum physics. A particle’s tunneling (verb) is due to a solution to the renormalization of its quantum wave function associated with a particular observation. This event doesn’t create a tunnel (noun) that other particles may use the way a car can pass through a tunnel dug through a mountain by a tunneling machine.

The suggestion that the probability of Quantum tunnelling resulting in a series of observations of a particle over time exhibiting a speed in excess of c is, I believe, incorrect.

hyperspace (hyper-luminous expansion) is Minkowski spacetime. (wiki)

Although he term “hyperspace” is a common synonym for Minkowski space, is not in the same sense synonymous with “hyper-luminous expansion”. It’s important to distinguish between the usage of the term in this sense, and others, such as as it is commonly used in science fiction, to refer to a means by which objects such as spacecraft can travel faster than the speed of light. Minkowski space is a mathematical physics theoretical formalism. “Hyperspace” in its most common usage is, as the preceeding wikipedia link states “a fictional plot device”. The scientific acceptance of the former does not imply the scientific acceptance of the latter.

### #319 Fatstep

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Posted 08 August 2007 - 03:52 AM

I just stumbled upon this, and it says the light is caused by particles going faster than light in that medium, that's faster than light, and then slowing down.

ÄŒerenkov radiation - Wikipedia, the free encyclopedia

### #320 riper

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Posted 08 August 2007 - 10:14 AM

nothing that we discoverd can move faster than the light. that is if u are talking about the movement. bu speed of light is not the fastest. if u are talkig about just geting from point A

### #321 riper

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Posted 08 August 2007 - 10:24 AM

are talking about speed, or movemet ? because is not thesame thing. ligt is the fastest source moving. but i case of speed ( things that hapen per second / microsecond or less ) there are faster things e.g mind.................................................................

### #322 ronthepon

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Posted 08 August 2007 - 10:30 AM

I just stumbled upon this, and it says the light is caused by particles going faster than light in that medium, that's faster than light, and then slowing down.

ÄŒerenkov radiation - Wikipedia, the free encyclopedia

Yeah, but it's for faster in light in the medium.

### #323 riper

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Posted 08 August 2007 - 11:48 AM

i know its sounds funny but do u thing that is possible to create something that flyes with speed of light out of the elements fgound on earth. is there any strong metal or aloy that can withsdand it ?