# Why can't energy or information go faster than light?

Dale
Mentor
2020 Award
If information could go faster than light then according to relativity you could violate causality. Out of relativity, faster than light, and causality, you can only have two. It looks like this universe has relativity and causality, so it cannot have FTL

Imager and vanhees71
FactChecker
Gold Member
Experiments show that there is a speed, c, that is not exceeded when the speed of a platform is added to the speed of light and other electromagnetic waves. This forces there to be a trade-off between motion in space dimensions and motion in time. That, in turn, forces the mathematical geometry of space-time where there is no speed greater than c. In that geometry, with that speed/time trade-off, there is no such thing as a speed greater than c.

danielhaish
phinds
Gold Member
... why cant information go faster then the light or energy
How do you propose that information be transferred? By magic? If not, then you have 2 choices to use for transferring the information and they are massless device (such as light) or massive devices (such as electrons). You already state that neither on of those can travel faster than light so why would you think that information should be able to travel faster than light?

Klystron, vanhees71, martinbn and 5 others
Nugatory
Mentor
but why cant information go faster then the light or energy
If information could move from point A to point B faster than the speed of light then we could arrange things in such a way that in some frames the message arrives at point B before it has been sent. With a bit more cleverness (google for "Tachyonic Anti-telephone") , we can arrange things in such a way that after receiving the message the recipient will be able to destroy the sending mechanism before the message has been sent.

The resulting contradictions and paradoxes are a very convincing argument that the universe operates under laws that don't allow faster-than-light causality.

Glenn G, vanhees71 and PeroK
jbriggs444
Homework Helper
If information could move from point A to point B faster than the speed of light then we could arrange things in such a way that in some frames the message arrives at point B before it has been sent. With a bit more cleverness (google for "Tachyonic Anti-telephone") , we can arrange things in such a way that after receiving the message the recipient will be able to destroy the sending mechanism before the message has been sent.

The resulting contradictions and paradoxes are a very convincing argument that the universe operates under laws that don't allow faster-than-light causality.
The techyonic anti-telephone argument depends on the principle of relativity -- that the laws of physics are the same no matter what inertial frame we use. In particular, it makes use of that principle when we argue about the behavior of the outbound leg of the anti-telephone using one frame and then argue about the behavior of the return leg using a different frame.

If a magical undiscovered FTL effect were to exist and were to allow for transfer of actionable information then we could, in principle, salvage causality by sacrificing the principle of relativity. The FTL effect could respect some preferred frame within which the FTL signal never goes backward in time.

However, the principle of relativity is at the core of most of our theories about the universe. Giving it up would require some extraordinary evidence.

vanhees71 and PeroK
The techyonic anti-telephone argument depends on the principle of relativity -- that the laws of physics are the same no matter what inertial frame we use. In particular, it makes use of that principle when we argue about the behavior of the outbound leg of the anti-telephone using one frame and then argue about the behavior of the return leg using a different frame.

If a magical undiscovered FTL effect were to exist and were to allow for transfer of actionable information then we could, in principle, salvage causality by sacrificing the principle of relativity. The FTL effect could respect some preferred frame within which the FTL signal never goes backward in time.

However, the principle of relativity is at the core of most of our theories about the universe. Giving it up would require some extraordinary evidence.
But this signle doest really go through distance becuase you can't catch it in the middle so is valocty is still may be lower then light becuase then let say there is minimal distance you can move when a phenomenon like gravity is expends then it goes through all space so it go from point a to b then to c and so on so it go some distance so you can say that it speed is d/t distance/time but if the signal is coming through only.two point the distance it travels is very small so also the valocty is not necessary faster thenight am I right?

jbriggs444
Homework Helper
But this signle doest really go through distance becuase you can't catch it in the middle so is valocty is still may be lower then light
You can't weasel out of it that easily. Regardless of what the signal does or does not do in the middle, if it gets to the end of its journey ahead of a light speed signal, if it can convey actionable information and if the laws of special relativity hold good, paradoxes ensue.

vanhees71
Dale
Mentor
2020 Award
But this signle doest really go through distance becuase you can't catch it in the middle so is valocty is still may be lower then light becuase then let say there is minimal distance you can move when a phenomenon like gravity is expends then it goes through all space so it go from point a to b then to c and so on so it go some distance so you can say that it speed is d/t distance/time but if the signal is coming through only.two point the distance it travels is very small so also the valocty is not necessary faster thenight am I right?

Staff Emeritus
Daniel, your messages are incomprehensible. Whatever language is your first language, it uses sentences. So does English. Second, you got an excellent message in #4. You should read it and think about it.

Grasshopper, PeroK and danielhaish
Can I try to rewrite it in new thread?

Dale
Mentor
2020 Award
Can I try to rewrite it in new thread?

Nugatory
Mentor
The techyonic anti-telephone argument depends on the principle of relativity
Indeed it does. That's why I said "very convincing argument" instead of "proof". It's not a proof because we haven't excluded the possibility that some of our basic beliefs about the universe (homogeneity, isotropy, principle of relativity, ...) are wrong. There's another assumption as well, namely that the universe doesn't allow causal paradoxes such as the anti-telephone.

I consider any argument that is valid as long as these assumptions are valid to be very convincing.

Grasshopper, vanhees71, jbriggs444 and 2 others
Indeed it does. That's why I said "very convincing argument" instead of "proof". It's not a proof because we haven't excluded the possibility that some of our basic beliefs about the universe (homogeneity, isotropy, principle of relativity, ...) are wrong. There's another assumption as well, namely that the universe doesn't allow causal paradoxes such as the anti-telephone.

I consider any argument that is valid as long as these assumptions are valid to be very convincing.
They might be both true according to some theory dont they

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Sorry can't edit the thread any more but I will rewrite the post here as another post

PeroK
Homework Helper
Gold Member
2020 Award
But this signle doest really go through distance becuase you can't catch it in the middle so is valocty is still may be lower then light becuase then let say there is minimal distance you can move when a phenomenon like gravity is expends then it goes through all space so it go from point a to b then to c and so on so it go some distance so you can say that it speed is d/t distance/time but if the signal is coming through only.two point the distance it travels is very small so also the valocty is not necessary faster thenight am I right?
I was going to nominate this for the most incomprehensible message of the week, but I see that @jbriggs444 could make some sense of it.

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Grasshopper
I was going to nominate this for the most incomprehesible message of the week, but I see that @jbriggs444 could make some sense of it.
I am working on re write sorry I don't find it so easy

But this single doesn't really go through distance because you can't catch it in the middle from location A to location B so is valocity is still may be lower then light because then let say there is minimal distance object can move. when a phenomenon like gravity is expends then it goes through all space so it go from point a to b then to c and so on, so it go some distance so you can say that it speed is d/t distance/time but if the signal is coming through only.two point the distance it travels is very small so also the valocity is not necessary faster then light am I right?
is it batter now ?

Grasshopper
jbriggs444
Homework Helper
I see that you have corrected the spelling of "because" on the first line. The spelling of "valocity" is still incorrect.

I see you have changed from having you move to having an object move.

I see you have added a period so that we have two sentences instead of one.

So far, this is not a significant re-write.

The first thought I'd had was that you were thinking of something like quantum mechanics. That if a signal goes straight from point a to point b without being intercepted in the middle that it cannot properly be said to have a velocity at all. But it seems that is not what you are trying to express.

My next thought is that you are talking about something like "folding" space up so that instead of going the long way from point a to point b to point c and eventually on to the target at point z, a signal goes straight from point a to point z over a shorter, direct path that does not follow the folded, crumpled up surface.

Assuming the latter is what you have in mind you will have to describe this hypothetical capability in more detail. Is it possible to fold space-time to link any two events that are space-like separated?

phinds
Gold Member
is it batter now ?
No, "batter" is stuff you use to make cakes or cookies. I realize that English is apparently very difficult for you, but still ...

Staff Emeritus
is it batter now ?

You're battering the English language, that's for sure.

I used to think the problem was a language barrier. I am coming to the conclusion that the reason you can't express what you are thinking is because it is not clear in your own mind. Not because you dropped a period into the middle of a run-on sentence.

Grasshopper
PeroK
Homework Helper
Gold Member
2020 Award
No, "batter" is stuff you use to make cakes or cookies. I realize that English is apparently very difficult for you, but still ...
With traditional British fish and chips, the fish comes in batter (the green stuff is "mushy peas"):

Grasshopper
phinds
Gold Member
... "mushy peas"
And THAT is a good example of why people say bad things about British food.

jbriggs444
Homework Helper
Batter eat it quick before the wife catches you breaking the diet.

Grasshopper and Dale
I see that you have corrected the spelling of "because" on the first line. The spelling of "valocity" is still incorrect.

I see you have changed from having you move to having an object move.

I see you have added a period so that we have two sentences instead of one.

So far, this is not a significant re-write.

The first thought I'd had was that you were thinking of something like quantum mechanics. That if a signal goes straight from point a to point b without being intercepted in the middle that it cannot properly be said to have a velocity at all. But it seems that is not what you are trying to express.

My next thought is that you are talking about something like "folding" space up so that instead of going the long way from point a to point b to point c and eventually on to the target at point z, a signal goes straight from point a to point z over a shorter, direct path that does not follow the folded, crumpled up surface.

Assuming the latter is what you have in mind you will have to describe this hypothetical capability in more detail. Is it possible to fold space-time to link any two events that are space-like separated?
actually it is what I am trying to express

Grasshopper