light speed

[jamey2k9]

it's said that light speed is the fastest possible speed for anything to travel at but why is that couldn't somthing move faster light speed if so what

all comments welcome

[insane_alien]

well there are hypothetical particles called tachyons which wouldn't be able to move slower than light.

 

but the main point is that in either case it would take infinite energy to accelerate to the speed of light as the closer you get the more energy you need to put in to go 1m/s faster.

[NowThatWeKnow]

The expansion of space can cause two galaxies to separate from each other faster then the speed of light. However, the common belief is that any thing with mass is restricted to less then light speed because of what insane_alien said.

Edited March 1, 2009 by NowThatWeKnow

[cameron marical]

what about some unkown or possibly known, massless particle. like a photon, or something along those lines. are photons the only true massless particles? but, i agree, why doesnt something go faster than light. what makes that wall. ya, we couldnt see it, so maybe there already is tons of particles like that.

[PrinceOfDragons]

Maybe we cannot see these particles cause they do go faster than light?

[Airbrush]

Maybe so, and Mr. Alien pointed out they are called "tachyons", but how do you propose we can detect them?

 

What is that kind of particle that can travel through light years of solid lead, like a hot knife thru butter?

 

Dark matter cannot be seen, and it doesn't even move.

[insane_alien]

Maybe so, and Mr. Alien pointed out they are called "tachyons", but how do you propose we can detect them?

 

personally, i don't think they exist. however, i am in no way qualified for that to be anymore than opinion. i would have no idea how to detect them, i doubt anybody else would either.

 

What is that kind of particle that can travel through light years of solid lead, like a hot knife thru butter?

 

neutrinos. and knifes cut, neutrinos don't, they just pass through it as if it wasn't there.

 

i think its a light year of lead(approximately) to block half the flux of neutrons.

 

Dark matter cannot be seen, and it doesn't even move.

 

it can't be seen because it doesn't interact electromagnetically but it does move. there is nothing for them to fix onto.

[Airbrush]

Mr. Alien, my question about detecting tachyons was for the poster who was hypothesizing about them. Sorry for the misunderstanding.

 

I will be carefull to not try to cut anything with neutrinos.

 

Dark matter does whatever matter does, move or hang around. The point I was trying to make was that tachyons are not the only thing we cannot pin down as we like to.

[Klaynos]

IIRC tachyons would radiate in a very distinctive way that we could detect. This has never been observed, you'd also need some event that could create them without accelerating past light speed.

[SkepticLance]

There is often a bit of misunderstanding on this. It is not that anything cannot go faster than light - it is that nothing can accelerate to light speed. It is a bar to acceleration - not velocity. To accelerate something to light speed would take infinite energy - hence impossible.

 

Tachyons are hypothetical particles that were created at a speed greater than light. They go faster than light because they have never had to accelerate through the light barrier, which would take infinite energy. However, as pointed out before, tachyons so far, are purely imaginary particles. They have never been detected. Nor do we know of any way to detect them. They are theoretically possible, but there is no theoretical impetus to suggest they have to exist.

[Janus]

There is often a bit of misunderstanding on this. It is not that anything cannot go faster than light - it is that nothing can accelerate to light speed. It is a bar to acceleration - not velocity. To accelerate something to light speed would take infinite energy - hence impossible.

 

Tachyons are hypothetical particles that were created at a speed greater than light. They go faster than light because they have never had to accelerate through the light barrier, which would take infinite energy. However, as pointed out before, tachyons so far, are purely imaginary particles. They have never been detected. Nor do we know of any way to detect them.

 

Yes there is a method to detect tachyons if there were to exist: Cerenkov radiation. When a charged particle travels through a medium at speeds greater than that of light in the medium, it produces a distinctive visible light. It is like a photonic shock wave.(This likely to be what Klaynos was referring to).

 

One could detect a tachyon by noting Cerenkov radiation originating in a vacuum.

[SkepticLance]

Janus.

That is fine, but purely theoretical. Attempts have been made to detect tachyons, without success. Until we prove empirically we can detect tachyons, we cannot detect tachyons.

[Klaynos]

Janus.

That is fine, but purely theoretical. Attempts have been made to detect tachyons, without success. Until we prove empirically we can detect tachyons, we cannot detect tachyons.

 

It is evidence against tachyons.

 

Thanks for reminding me it was Cherenkov radiation, which I am very familiar with but had forgotten the connection in this case.

 

Cherenkov radiation is very well understood and observed for non-tachyon matter. It is also predicted to have to exist for tachyons (assuming they are charged, which there is no reason why they should be charged or neutral), we've never detected any from tachyons so either we're missing something or they don't exist.

 

The jury is still out on whether they exist or not, all that can be said at present is there is no evidence for them existing.

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It's also imo important to formulate some method that they could be created moving at a speed faster than c without acceleration.

[ydoaPs]

It's also imo important to formulate some method that they could be created moving at a speed faster than c without acceleration.

 

Couldn't they be created in a method similar to how photons are created moving at c without being accelerated?

[Klaynos]

Couldn't they be created in a method similar to how photons are created moving at c without being accelerated?

 

Not without moving only at c as photons and gravitons (assuming the exist) do.

[Xittenn]

Cherenkov radiation is very well understood and observed for non-tachyon matter. It is also predicted to have to exist for tachyons (assuming they are charged, which there is no reason why they should be charged or neutral

 

Why do you say assuming they are charged? The Wiki on Tachyons clearly states that even if they are neutral a gravitational 'Cherenkov Radiation' could be observed.

 

oh and.............

http://en.wikipedia.org/wiki/Superbradyon

[ydoaPs]

Not without moving only at c as photons and gravitons (assuming the exist) do.

 

What's the mechanism by which THEY get from zero to c without accelerating? What would prevent tachyonic matter from getting to >c without accelerating?

[Klaynos]

What's the mechanism by which THEY get from zero to c without accelerating? What would prevent tachyonic matter from getting to >c without accelerating?

 

They're massless. It's a requirement IIRC... Need to reread some QED though to answer you fully...

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Why do you say assuming they are charged? The Wiki on Tachyons clearly states that even if they are neutral a gravitational 'Cherenkov Radiation' could be observed.

 

oh and.............

http://en.wikipedia.org/wiki/Superbradyon

 

Gravitational Cherenkov Radiation, is not something I'm overly familiar with, but if it's what I think it is, then I doubt our gravity waves are capable of detection currently? The range of things we can observe with ground based detectors only includes very very large events.

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As for Superbradyon, I'll have a look for some non-arXiv papers on monday.... They're not something I've heard of before.

[cameron marical]

how could tachyons be created? how can you create something that starts off moving faster than c.

[Xittenn]

They're massless. It's a requirement IIRC... Need to reread some QED though to answer you fully...

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Gravitational Cherenkov Radiation, is not something I'm overly familiar with, but if it's what I think it is, then I doubt our gravity waves are capable of detection currently? The range of things we can observe with ground based detectors only includes very very large events.

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As for Superbradyon, I'll have a look for some non-arXiv papers on monday.... They're not something I've heard of before.

 

The wiki just said this........

 

A charged tachyon traveling in a vacuum therefore undergoes a constant proper time acceleration and, by necessity, its worldline forms a hyperbola in space-time. However, as we have seen, reducing a tachyon's energy increases its speed, so that the single hyperbola formed is of two oppositely charged tachyons with opposite momenta (same magnitude, opposite sign) which annihilate each other when they simultaneously reach infinite velocity at the same place in space. (At infinite velocity the two tachyons have no energy each and finite momentum of opposite direction, so no conservation laws are violated in their mutual annihilation. The time of annihilation is frame dependent.) Even an electrically neutral tachyon would be expected to lose energy via gravitational Cherenkov radiation, since it has a gravitational mass, and therefore increase in velocity as it travels, as described above.

 

Rereading it I may have misinterpreted the meaning.................it may not have been so clear.

 

I do believe the Superbradyon is a hypothetical Supersymetry particle, a product of String Theory.............I'm still avoiding any literature on this topic!

 

Reverse Cherenkov Radiation hmmmmmmm Metamaterials............

Edited March 15, 2009 by buttacup

[Airbrush]

The probable reason we cannot detect tachyons is because they could only be created by the Big Bang and therefore are already long gone outside our visual horizon.

[Martin]

The probable reason we cannot detect tachyons is because they could only be created by the Big Bang and therefore are already long gone outside our visual horizon.

 

I don't understand your reasoning, Airbrush.

 

I don't have much faith in the existence of tackies, but suppose they did exist and suppose a bunch were created along with some other stuff shortly after the beginning of expansion.

 

Why wouldn't they be whizzing by here at this moment?

 

If the big bang volume was finite, then space today is finite, and the taxies could have circled around perhaps several times already. Depending on their speed relative to expansion. Think about the balloon model with speckles on the balloon being galaxies. And stuff like photons and the rest moving across the surface.

 

On the other hand, if space is infinite, then the big bang volume also was infinite. This is standard cosmology I'm telling you. So there are plenty of tachyons coming our way, plenty here now, and lots that have already passed us.

 

That is, if tachyons actually exist and if a bunch were produced right after the start of expansion.

 

You seem to disagree! What is your argument?

[Airbrush]

Thanks for asking. If tackies were created at the Big Bang, and they were like neutrinos, then they would have flown "away" from the Bang, outracing everything else. If anybody got in front of them they would nearly instantly pass thru them. If there was no wall to bounce off? What if tackies were like neutrinos and penetrated any "wall" with ease?

 

Maybe even supernovas create tackies, or even black holes, but we don't recognize their signature.

[SkepticLance]

There is another possibility. If tachyons do not interact with normal matter and do not create a gravitational field, then they are indetectable - and we have not been able to detect them, so this idea is compatible with observation.

 

For all we know, there may be an entire tachyon universe intersecting our own. With no interaction - why not?

[Martin]

Thanks for asking. If tackies were created at the Big Bang, and they were like neutrinos, then they would have flown "away" from the Bang, outracing everything else.

 

But we expect to be able to detect neutrinos from the big bang, from some fraction of a second after start.

 

We just need to get the right instruments to detect neutrinos of the right energy. The energy range has been calculated---I forget what it is.

 

Please read my post again. There is no way that those particles could have "run away". Whatever hasn't gotten absorbed and changed by collision is still here.

 

There is no empty space for them to run away into.

 

It sounds like you are still suffering from the "explosion" misconception. Conventional bigbang cosmology is in no sense pictured as an explosion of stuff flying out from some central point.

 

If it were like that then the CMB photons from 380,000 years after start of expansion would also have "flown away". Everything would be flying outwards from some point, out into empty space.

 

That is not how it is, Airbrush. That is a popular misconception. Get over it .

You could try reading Lineweaver's SciAm article "Misconceptions about the Big Bang" again. Have you at least read it once?

Here's the link. It's also in my sig. Scroll down. The first page or so of the pdf file is blank.

http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf

 

Here's an alternative link that doesn't have the blank page at the beginning.

http://www.astro.princeton.edu/~aes/AST105/Readings/misconceptionsBigBang.pdf

Edited March 17, 2009 by Martin