Relative Mass

[Chirios]

Things cannot go faster than the speed of light due to the fact that the closer they approach light speed, the more mass they gain, so could a theoretical massless particle, (call it a Chirion) move faster than the speed of light?

 

[Master_Ghost_Knight]

No I don't think so, the equations of general theory of relativity that describes the relative motion doesn't allow it.
Altough some sugest otherwise.

 

[Josan]

Aren't photons massless particles? And don't they move AT the speed of light as a result?

 

[Master_Ghost_Knight]

Aren't photons massless particles? And don't they move AT the speed of light as a result?

But not faster than.

 

[yarps]

From the point of view of Special Relativity, there is a one-to-one relation between the allowed speeds for a particle, and the square of its mass:

• 
  Positive mass squared -> Speed must be less than the speed of light
  Zero mass squared -> Particle travels exactly at the speed of light
  Negative mass squared -> Particle must travel faster than the speed of light (and consequently, backwards in time).

Members of the last category are sometimes called tachyons.

However, from the point of Quantum Field Theory, a negative mass squared corresponds to an instability; the universe will shift to a different quantum state, where the particle has a positive (or zero) mass squared. The reasons are somewhat technical. However, it is well understood with QFT, and would seem to show that there are no physical tachyons.

 

[JacobEvans]

I've asked my physics teacher, and he said tachyon always move faster than the speed of light but can't go slower.

 

[Squagnut]

I've asked my physics teacher, and he said tachyon always move faster than the speed of light but can't go slower.

Indeed tachyons may even exist in a universe of three temporal dimensions and one spatial dimension, tho' anything which moves faster than light will always appear to go backwards in time. They're a tad tricky to pin down, since they disappear before they exist.

 

[JacobEvans]

Indeed tachyons may even exist in a universe of three temporal dimensions and one spatial dimension, tho' anything which moves faster than light will always appear to go backwards in time. They're a tad tricky to pin down, since they disappear before they exist.

He also told me that they don't necessarily go backwards in time, since the time part of the equation will end up being the square root of negative number(imaginary number), not just a plain old negative number. So it would work in a weird way that I'm not qualified to answer much further, other than it would probably not go back in time in the regular sense.

 

[Einstein's_Advocate]

Things cannot go faster than the speed of light due to the fact that the closer they approach light speed, the more mass they gain, so could a theoretical massless particle, (call it a Chirion) move faster than the speed of light?

No, and here's why:

"A particle has a positive mass" <=> "This particle is traveling with a speed less than the speed of light"
"A particle has no mass" <=> "This particle is traveling at the speed of light"

Please note, this is an if and only if statement, i.e. "If a particle has zero mass, it is necessarily traveling at the speed of light" (But not faster, precisely the speed of light!)


There are equations which demonstrate why this is in special relativity.

 

[IrBubble]

It's fairly easy to demonstrate, atleast in the SR that moving faster than the speed of light is impossible, and I don't know how this checks out in GR, but as it seems to be a layman answer you're looking for I hope my layman answer will provide some insight

The special relativity uses the lorenz factor to calculate the dilutation in time and space. The lorenz factor is

Where V is the velocity, and C is the speed of light. If V> C than you get a negative root, which means it's imaginary, thus anything mulitplied by this factor will also be.

 

[Zylstra]

is there any evidence for tachyons?

 

[e2iPi]

is there any evidence for tachyons?

There has been no evidence for or against the existence of tachyons as a literal particle.

In the realm of SR, there is the Feinberg principal which, interestingly enough, predicts that any tachyon traveling backwards in time could would be indistinguishable from a tachyon traveling forward in time. So any tachyon detector which we built would look to us like a tachyon emitter. So tachyons (if they do indeed exist as a literal particle) cannot be used to violate causality.

Tachyon fields do exist, at least in the realm of quantum field theory, however every one of them is an example of spontaneous symmetry breaking. The field exists in a maximum rather than minimum state. This is a very unstable field and will fall to the local minimum with exponentially increasing amplitude. This is called tachyon condensation. The phraseology gives the impression that there is a physical quanta involved with an imaginary mass, however once the field reaches a local minimum, its quanta will have a positive mass. the Higgs mechanism is an example of this.

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[IrBubble]

In the realm of SR, there is the Feinberg principal which, interestingly enough, predicts that any tachyon traveling backwards in time could would be indistinguishable from a tachyon traveling forward in time.

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If they travel forward in time, don't they defy relativity, since travelling forward in time with superluminal velocity should not be possible? Or is this just a principle to visualize the phenomenon and explain how causality is not broken?

 

[Master_Ghost_Knight]

If they travel forward in time, don't they defy relativity, since travelling forward in time with superluminal velocity should not be possible? Or is this just a principle to visualize the phenomenon and explain how causality is not broken?

The ones that look like moving forward will also look to move slower.

 

[e2iPi]

The ones that look like moving forward will also look to move slower.

That is probably the most intuitive way to look at the problem.
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