# Time and the Sound Barrier: How Fast is Too Fast?

• Tjl
I'm not sure what it would have velocity since it is in a different reference frame, but it would not be c. In summary, according to physics, there are no tachyons, light does not "lag" behind objects as they travel faster, and time would not be affected if you exceeded the speed of light.f

#### Tjl

When an object breaks the sound barrier, sounds "lag" behind that object as it travels faster, theoretically the same can be said for light. Would this work the same for time? If you exceeded whatever limit this barrier has would time "lag" behind you?

Tjl said:
When an object breaks the sound barrier, sounds "lag" behind that object as it travels faster, theoretically the same can be said for light.
No, you cannot pass the speed of light. There are a number of ways to show this, possibly the most relevant in this case is the relativistic addition of velocities:$$v_{AC}=\frac{v_{AB}+v_{BC}}{1+\frac{v_{AB}v_{BC}}{c^2}}$$. From this, you can see that any time you add two speeds which are less than the speed of light, the result will always be less than the speed of light.
Tjl said:
Would this work the same for time? If you exceeded whatever limit this barrier has would time "lag" behind you?
I'm confused about what you're asking. Are you proposing moving faster through time than time itself? Relativity allows you to change your "speed through time" (which can be quite a confusing phrase) with respect to other observers, but time for you still continues on as normal.

it would certainly do, but unlike u(tjl) said. it is relative so one observer/listener at the end of a train and next at the head(i don't know what u call the place where the driver;if there is one; sits in the train) of the train can hear the sound of "a" gun shot at different times! may be this is it. if not, i don't know.

regards
gurkha-war-horse

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It was purely theoretical, and not to dispute, but your statement is incorrect. Nobody knows if tachyons do in fact exist, and until a credible theory can be raised, faster then light travel or communication cannot be disproved.

gurkhawarhorse said:
it would certainly do, but unlike u(tjl) said. it is relative so one observer/listener at the end of a train and next at the head(i don't know what u call the place where the driver;if there is one; sits in the train) of the train can hear the sound of "a" gun shot at different times! may be this is it. if not, i don't know.

regards
gurkha-war-horse
Also, that is only taken into effect if the train was moving at near the speed of light.

Tjl said:
It was purely theoretical, and not to dispute, but your statement is incorrect. Nobody knows if tachyons do in fact exist, and until a credible theory can be raised, faster then light travel or communication cannot be disproved.

You asked a question about physics, and you got the answer according to physics. According to physics, there are no tachyons.

There are also no unicorns.

Tjl said:
It was purely theoretical, and not to dispute, but your statement is incorrect. Nobody knows if tachyons do in fact exist, and until a credible theory can be raised, faster then light travel or communication cannot be disproved.
I did not say tachyons do not move faster than the speed of light if they exist. I said you cannot move faster than the speed of light; you are not composed of tachyons.

I slipped the word you in there :( That is my mistake sorry. I meant any object or particle or tachyon.

Tjl said:
Also, that is only taken into effect if the train was moving at near the speed of light.
NO!
it is actually at all motions (ofcourse relative) but is much effective at high speed(ie. not only at 0.99c/near the speed of light). But u can't deny that it happens even in lower ones.
:tongue2: :tongue: :yuck: :tongue2:
let me remind u what DrChinese said/wrote "there are no unicorns". :rofl:
gurkha-war-horse

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Tjl said:
I slipped the word you in there :( That is my mistake sorry. I meant any object or particle or tachyon.
Well then, hypothetically speaking, if you're asking if light "lags" behind a tachyon in a tachyon's own reference frame, the answer is still no. A tachyon will still see a light beam as moving at c. This follows naturally from the second postulate of special relativity, but to reemphasize the point we can solve the relativistic addition of velocities equation (in relativistic units) $$v_{AC}=\frac{v_{AB}+v_{BC}}{1+v_{AB}v_{BC}}$$ for a tachyon (A) which has velocity $$v_{BA}=3$$ relative to some standard matter particle (B). From the tachyon's reference frame (if I am allowed to do such things; I haven't read much about tachyons, so corrections may be needed) particle B will have velocity $$v_{AB}=-3$$, and of course a photon (C) in particle B's reference frame will have $$v_{BC}=1$$, so in the tachyon's (A's) reference frame, the photon (C) will have velocity $$v_{AC}=\frac{-3+1}{1-3}=1$$.

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