[webplodder]

If it is found that neutrinos do violate the faster-than-light barrier how would that destroy the notion of causality?

[Schrödinger's hat]

webplodder, on 21 October 2011 - 11:11 AM, said:

If it is found that neutrinos do violate the faster-than-light barrier how would that destroy the notion of causality?

Well assuming they move faster than light, and that relativity holds.
Sending something faster than light in one frame is the same as sending a message back in time in another.
Once you can send a message back in time you run into all sorts of things like the grandfather paradox.

If this isn't enough I can try and explain exactly how it entails sending a message back in time,

[Ophiolite]

If you are in the UK may I recommend the BBC documentary aired two days ago and available, I would think, on iplayer "Faster Than the Speed of Light". It is one of the best science documentaries I have seen for a long time, providing a balanced view of the neutrino issue. It also contained this causality joke:

The bartender said "We don't serve neutrinos in here."

A neutrino walks into a bar.

[webplodder]

Schrödinger, on 21 October 2011 - 12:49 PM, said:

Well assuming they move faster than light, and that relativity holds.
Sending something faster than light in one frame is the same as sending a message back in time in another.
Once you can send a message back in time you run into all sorts of things like the grandfather paradox.

If this isn't enough I can try and explain exactly how it entails sending a message back in time,

Please do.

Ophiolite, on 21 October 2011 - 01:34 PM, said:

If you are in the UK may I recommend the BBC documentary aired two days ago and available, I would think, on iplayer "Faster Than the Speed of Light". It is one of the best science documentaries I have seen for a long time, providing a balanced view of the neutrino issue. It also contained this causality joke:

The bartender said "We don't serve neutrinos in here."

A neutrino walks into a bar.

I did see that documentary but it seemed to leave unanswered questions.

[Mystery111]

webplodder, on 21 October 2011 - 11:11 AM, said:

If it is found that neutrinos do violate the faster-than-light barrier how would that destroy the notion of causality?

It's all about relativity. If you go fast enough, you can slow down time. If you could move at lightspeed, time would completely stop. If you could go faster than light speed (and still believing that Einstein's laws hold true up to this point) then you could potentially oscillate through time. In effect, you could violate standard laws of cause and effect, action and reaction.

[Ophiolite]

webplodder, on 21 October 2011 - 01:38 PM, said:

I did see that documentary but it seemed to leave unanswered questions.

A key point of the documentary was that if those neutrinos are travelling faster than light then there will be a galaxy load of unanswered questions. Which specific ones did you have in mind?

[swansont]

There is currently a thread on why FTL destroys causality
http://www.sciencefo...lity-violation/

[DrRocket]

Mystery111, on 21 October 2011 - 01:42 PM, said:

It's all about relativity. If you go fast enough, you can slow down time. If you could move at lightspeed, time would completely stop. If you could go faster than light speed (and still believing that Einstein's laws hold true up to this point) then you could potentially oscillate through time. In effect, you could violate standard laws of cause and effect, action and reaction.

Wrong.

If you look at the Lorentz transformations you will find that superluminal speeds result in imaginary time dilation.


What happens is that if superluminal information transfer were possible then the order of events is not preserved in all reference frames, resulting in effect preceding cause in some reference frames.

The following argument is taken from Essential Relativity by Rindler.

Fix points P and Q in spacetime and assume that a signal is sent from P to Q at some speed U>c. Choose a reference frame S such that the spatial coordinates of each lie on the x-axis. Select a second frame S' in standard orientation with respect to S moving relative to it at some velocity . Then in S'



For values of with one then has which means that in S' the signal is received before it is sent (i.e. P precedes Q in S but Q precedes P in S').

[webplodder]

Mystery111, on 21 October 2011 - 01:42 PM, said:

It's all about relativity. If you go fast enough, you can slow down time. If you could move at lightspeed, time would completely stop. If you could go faster than light speed (and still believing that Einstein's laws hold true up to this point) then you could potentially oscillate through time. In effect, you could violate standard laws of cause and effect, action and reaction.

Ok, so is it the case that the faster you go the more massive you become and, therefore, the slower you move? That at the speed of light you would become infinitely massive so that no movement or time would exist? If so, how could a particle like the neutrino, which I understand does possess a little mass, get past this barrier? Even a tiny amount of mass would become infinite at light speed, wouldn't it?

Ophiolite, on 21 October 2011 - 02:35 PM, said:

A key point of the documentary was that if those neutrinos are travelling faster than light then there will be a galaxy load of unanswered questions. Which specific ones did you have in mind?

The one about causality was the main one.

This post has been edited by webplodder: 21 October 2011 - 03:52 PM

[DrRocket]

webplodder, on 21 October 2011 - 03:52 PM, said:

The one about causality was the main one.

Causility would be violated in special relativity if it were possible to send "information" at superluminal speeds. That is the reason that relativists proscribe such possibilities.

But if a particle can travel at superluminal speed, then the logical foundation for special relativity is violated, and all bets are off. You then have a great deal of empirical evidence, but the theoretical explanation is no longer valid.

There is no such causality problen in Newtonian mechanics. The problem is that Newtonian mechanics disagrees with experiment when high speeds are involved. IF neutrinos really traveled at speed greater than c we will now have a massive disconnect between relativity and experiment. That is a BIG deal.

[michel123456]

DrRocket, on 21 October 2011 - 03:42 PM, said:

(...)
What happens is that if superluminal information transfer were possible then the order of events is not preserved in all reference frames, resulting in effect preceding cause in some reference frames.
(...)

So in some reference frame the measured observation would be that some event happen randomly, without any cause, and some instant later, the cause appears. That does not sound too outrageous. In fact that could explain apparent randomness.

[webplodder]

DrRocket, on 21 October 2011 - 04:08 PM, said:

Causility would be violated in special relativity if it were possible to send "information" at superluminal speeds. That is the reason that relativists proscribe such possibilities.

But if a particle can travel at superluminal speed, then the logical foundation for special relativity is violated, and all bets are off. You then have a great deal of empirical evidence, but the theoretical explanation is no longer valid.

There is no such causality problen in Newtonian mechanics. The problem is that Newtonian mechanics disagrees with experiment when high speeds are involved. IF neutrinos really traveled at speed greater than c we will now have a massive disconnect between relativity and experiment. That is a BIG deal.

Could this problem arise because we do not have a single theory that accounts for both classical physics and QM?

This post has been edited by webplodder: 21 October 2011 - 04:37 PM

[Appolinaria]

Particles exist.. not everything is just a wave. There is no cause before this effect, so I don't think it sounds crazy to think it's coming from the future.



Wouldn't this "effect before cause" actually explain our spontaneous existence? The birth of our universe? Lol.

This post has been edited by Appolinaria: 21 October 2011 - 05:37 PM

[webplodder]

Appolinaria, on 21 October 2011 - 05:14 PM, said:

Particles exist.. not everything is just a wave. There is no cause before this effect, so I don't think it sounds crazy to think it's coming from the future.



Wouldn't this "effect before cause" actually explain our spontaneous existence? The birth of our universe? Lol.

Well, if it is found that faster-than-light speed is possible then it could lend support to string theory which proposes that all known particles are simply objects called strings vibrating at different frequencies.

[Appolinaria]

webplodder, on 21 October 2011 - 06:31 PM, said:

Well, if it is found that faster-than-light speed is possible then it could lend support to string theory which proposes that all known particles are simply objects called strings vibrating at different frequencies.

Ah, I've heard of that theory before.... gotta read about it!

[DrRocket]

michel123456, on 21 October 2011 - 04:27 PM, said:

So in some reference frame the measured observation would be that some event happen randomly, without any cause, and some instant later, the cause appears. That does not sound too outrageous. In fact that could explain apparent randomness.

No.

Violation of causality is not randomness and randomness is not violation of causality.

A baseball player hitting a pitch before it is thrown is not random. It is bizarre, but not random.

Go read the post again. Pay attention to the mathematics.

[michel123456]

DrRocket, on 21 October 2011 - 09:12 PM, said:

No.

Violation of causality is not randomness and randomness is not violation of causality.

A baseball player hitting a pitch before it is thrown is not random. It is bizarre, but not random.

Go read the post again. Pay attention to the mathematics.

I don't understand where I am wrong.

You observe a baseball player hitting a pitch. Point. Maybe after 20 billion years you will observe someone throwing. The cause will appear so far from the result that you call the result "random", because there is no obvious observable cause. What is wrong with that?

This post has been edited by michel123456: 22 October 2011 - 09:01 AM

[Mystery111]

DrRocket, on 21 October 2011 - 03:42 PM, said:

Wrong.

If you look at the Lorentz transformations you will find that superluminal speeds result in imaginary time dilation.

Curious, I don't think I said anything about imaginary time dilation. I said it was able to oscillate in the time dimension.

That is to say, it freely able to move into the past and the future, obviously many causality problems arise.

Imaginary time is real space. Real time is imaginary space. Travelling at different speeds lets to travel through these descriptions of time.

webplodder, on 21 October 2011 - 03:52 PM, said:

Ok, so is it the case that the faster you go the more massive you become and, therefore, the slower you move? That at the speed of light you would become infinitely massive so that no movement or time would exist? If so, how could a particle like the neutrino, which I understand does possess a little mass, get past this barrier? Even a tiny amount of mass would become infinite at light speed, wouldn't it?

No because a tachyon would find the lowest amount of energy available for it at the speed of light. It's the effects of the speed which does not linearly move through the time. This is why when you send a tachyon off on it's journey, it could end up arriving at place before it had been fired.

[webplodder]

Quote

No because a tachyon would find the lowest amount of energy available for it at the speed of light. It's the effects of the speed which does not linearly move through the time. This is why when you send a tachyon off on it's journey, it could end up arriving at place before it had been fired.

Now you've lost me a bit. Is a tachyon the same as a neutrino?

[between3and26characterslon]

I'm sure everyone is aware of the experiment whereby a moicrowave signal was split in two and sent to two equidistant receivers. One of the signals was uninterupted whilst the other was blocked by a bar of copper. Upon closer examination of the osciloscope it was discovered that not only did a small signal make it through the copper block but it actually preceded the unhindered signal. The conclusion reported by the dimwits in the press was faster than light speed signals, the conclusion drawn by the scientists conducting the experiment was quantum tunneling (the early signal was exactly equivalent to the thickness of the copper block).

The point is, though the one signal did not "actually" travel faster than light it "effectively" travelled faster than light but it still arrived after it was sent... cause preceded effect.

If a tachyon is sent to a receiver 1Ly away it might only take 6 months to get there but it will still arrive 6 months after it was sent... cause still precedes effect.

The only problem arrises in the frame of the tachyon itself. It's only in its frame that effect precedes cause, that it arrives before it is sent.