Paradox? (split from Is FTL actually possible?)

[Moontanman]

23 minutes ago, Genady said:

Yes, it does. The electrons in your "phone", in the past, start moving without a physical cause.

A signal from the future is not a physical cause? Even if this is true how does it do any harm? Even if the signal to the past have no apparent physical cause how does this break physics any more than a an electron traveling FTL through water causing a glow that a man can see but not understand a break in physics?  

[Genady]

6 minutes ago, Moontanman said:

A signal from the future is not a physical cause? Even if this is true how does it do any harm? Even if the signal to the past have no apparent physical cause how does this break physics any more than a an electron traveling FTL through water causing a glow that a man can see but not understand a break in physics?  

The electron travelling faster than light in water does not break any physics because physics in fact says that it cannot move faster than the speed of light in vacuum.

Light itself does not set a limit. The limit is the speed, c. Light and any other massless particle move in vacuum with this speed, c. This is the connection to the "speed of light." 

[Moontanman]

3 minutes ago, Genady said:

The electron travelling faster than light in water does not break any physics because physics in fact says that it cannot move faster than the speed of light in vacuum.

Light itself does not set a limit. The limit is the speed, c. Light and any other massless particle move in vacuum with this speed, c. This is the connection to the "speed of light." 

I understand that, the lit is actually the speed of causality (as we know it) what I am asking is how would that cause problems in the real universe. The scenario I set up would not seem to bring about any paradoxes or cause any harm to the universe.  

[Genady]

Just now, Moontanman said:

I understand that, the lit is actually the speed of causality (as we know it) what I am asking is how would that cause problems in the real universe. The scenario I set up would not seem to bring about any paradoxes or cause any harm to the universe.  

This scenario breaks the laws of electrodynamics. It breaks the law of energy conservation. Etc. If such a scenario possible, the physics is all wrong.

[Moontanman]

26 minutes ago, Genady said:

This scenario breaks the laws of electrodynamics. It breaks the law of energy conservation. Etc. If such a scenario possible, the physics is all wrong.

If I understand correctly you are saying that the only consequence is breaking a law. Does this mean all of physics is wrong or that just a small subset of physics is wrong? I am not trolling, I am looking for physical consequences apart from just some subset of physics being wrong. Would a time "phone" just be something to be explained or would all of physics be wrong... I often get the impression that if just one thing was discovered that broke a law of physics then all of physics would be wiped clean instead of just needing to amend one thing.  

[Genady]

2 minutes ago, Moontanman said:

If I understand correctly you are saying that the only consequence is breaking a law. Does this mean all of physics is wrong or that just a small subset of physics is wrong? I am not trolling, I am looking for physical consequences apart from just some subset of physics being wrong. Would a time "phone" just be something to be explained or would all of physics be wrong... I often get the impression that if just one thing was discovered that broke a law of physics then all of physics would be wiped clean instead of just needing to amend one thing.  

Breaking laws of electrodynamics and energy conservation would be quite a big deal. It would lead to breaking of quantum electrodynamics, quantum field theory, gauge theory, standard model, thermodynamics, etc.

[MigL]

This is more usually stated as the 'grandfather paradox', Moon, and yes it does violate causality.

As usually stated, you go back in time and kill your grandfather. 
But then, you were never born to be able to go back in time.
So your grandfather still lives, you are born , and travel back to kill him.
But then you couldn't have ...

 This is the loop Sabine was talking about.

And it doesn't necessarily involve actual travel in time either.
Say you send a manuscript of Shakespeare's \\\romeo and Juliet back to William, who then publishes it, so that you, in the future, can send a copy back to him.
Who actually wrote Romeo and Juliet ?
What exactly 'caused' the play ?

[geordief]

If an object travelled back in time wouldn't every part of  it have to follow it on its journey?

There are so many components of any one object that it might  take longer than the age of this ,or multiple universes for that to happen.

If the object  arrived at the point in spacetime it had been at before minus one component it could not be said to have travelled  back in time

 

If  just one component  did manage to make the journey then that would be a quantum object and I wonder whether that would cause a problem ?

 

Would it be a case of "they all rolled over and one fell out,there was nine in the bed and the little one said....."?

[swansont]

2 hours ago, Moontanman said:

The scenario I set up would not seem to bring about any paradoxes or cause any harm to the universe.  

Scenarios that don’t cause issues aren’t the arguments that point to the impossibility of FTL signals. One could probably contrive a large number of scenarios that used FTL and didn’t cause other problems 

[Genady]

1 hour ago, geordief said:

If an object travelled back in time wouldn't every part of  it have to follow it on its journey?

They would rather travel back each to their own past, wouldn't they? So, they may even arrive there not as one object at all.

[geordief]

20 minutes ago, Genady said:

They would rather travel back each to their own past, wouldn't they? So, they may even arrive there not as one object at all.

There is that, as well (I mean I think you are right)

The  macro object that we are "sending back" has only existed as such for an infinitesimally short period of spacetime .

"It" has no time to return to in the past where it had the same configuration.

 

 

Edited April 9, 2023 by geordief

[dimreepr]

21 hours ago, Genady said:

Yes, it does.

Given the context of my post's is a paradox, can you explain how writing it down makes it true; FLT for example, would be made possible by "star wars", with that logic.

[Genady]

18 minutes ago, dimreepr said:

Given the context of my post's is a paradox, can you explain how writing it down makes it true; FLT for example, would be made possible by "star wars", with that logic.

I did not say anything about a paradox being true. I don't even know what it means.

[Moontanman]

16 hours ago, MigL said:

This is more usually stated as the 'grandfather paradox', Moon, and yes it does violate causality.

As usually stated, you go back in time and kill your grandfather. 
But then, you were never born to be able to go back in time.
So your grandfather still lives, you are born , and travel back to kill him.
But then you couldn't have ...

 This is the loop Sabine was talking about.

And it doesn't necessarily involve actual travel in time either.
Say you send a manuscript of Shakespeare's \\\romeo and Juliet back to William, who then publishes it, so that you, in the future, can send a copy back to him.
Who actually wrote Romeo and Juliet ?
What exactly 'caused' the play ?

The scenario I proposed wouldn't or at least shouldn't cause a time loop. 

16 hours ago, swansont said:

Scenarios that don’t cause issues aren’t the arguments that point to the impossibility of FTL signals. One could probably contrive a large number of scenarios that used FTL and didn’t cause other problems 

Thank you but I do understand that, what I am asking is would such a possibility require the retooling of all our science or would it just require a slight rethinking of certain concepts?  I remember when neutrinos had supposedly been found to be traveling FTL. The uproar was from a mild, things might need to be changed to running in circles like their hair was on fire, of course it turned out to be a mistake but it still left the question of what needed to be different for it to have been real unanswered.   

[swansont]

2 minutes ago, Moontanman said:

Thank you but I do understand that, what I am asking is would such a possibility require the retooling of all our science or would it just require a slight rethinking of certain concepts? 

Causality is a linchpin. Losing it would be a large upheaval.

 

2 minutes ago, Moontanman said:

I remember when neutrinos had supposedly been found to be traveling FTL. The uproar was from a mild, things might need to be changed to running in circles like their hair was on fire, of course it turned out to be a mistake but it still left the question of what needed to be different for it to have been real unanswered.

The response from the purported FTL neutrino signal among scientists was largely to look for the flaw in the experiment.

[Genady]

17 minutes ago, Moontanman said:

The scenario I proposed wouldn't or at least shouldn't cause a time loop. 

But it could.

[Moontanman]

3 minutes ago, swansont said:

Causality is a linchpin. Losing it would be a large upheaval.

Thank you, that was what I was looking for, I've been told that the scenario I proposed wouldn't break causality and therefore might be possible under some conditions as though breaking causality was the key that prevented communication through time not that the act itself was the problem and that breaking causality was the result not the problem.  

3 minutes ago, swansont said:

 

The response from the purported FTL neutrino signal among scientists was largely to look for the flaw in the experiment.

And rightly so. 

4 minutes ago, Genady said:

But it could.

How so? 

[Genady]

11 minutes ago, Moontanman said:

How so?

Give me a bit more detailed scenario and I'll try.

[Moontanman]

4 hours ago, Genady said:

Give me a bit more detailed scenario and I'll try.

There exists a time phone, it was created in 2020. In 2025 an asteroid hits in the atlantic ocean off the eastern seaboard of north america, millions die, Trillions of dollars in property damage occur. After the strike the phones is used to call 2024 and the extent of the damage is conveyed to the people of 2024, they evacuate the east coast and millions of lives are saved. The property damage still occurs but the lives are saved when the asteroid strikes. The phone call still occurs so the people can be saved from the threat that still happens. The Phone can only be used to call the time period that it exists in, no phone calls to before the phone exists. 

Edited April 10, 2023 by Moontanman

[Genady]

1 hour ago, Moontanman said:

There exists a time phone, it was created in 2020. In 2025 an asteroid hits in the atlantic ocean off the eastern seaboard of north america, millions die, Trillions of dollars in property damage occur. After the strike the phones is used to call 2024 and the extent of the damage is conveyed to the people of 2024, they evacuate the east coast and millions of lives are saved. The property damage still occurs but the lives are saved when the asteroid strikes. The phone call still occurs so the people can be saved from the threat that still happens. The Phone can only be used to call the time period that it exists in, no phone calls to before the phone exists. 

There is a terrorist group on the East Coast preparing a large-scale terrorist attack. When the asteroid hits, they die, among the other millions. Then the call is used and in 2024 they learn about the asteroid and the phone call. They evacuate and change their target so that in 2025, one minute before the call is made, the calling equipment is blown up. The call does not occur. People in 2024 don't know about the coming asteroid hit and don't evacuate. The millions, including the terrorists die. The terrorist attack does not occur. The call is made. People evacuate. Terrorists blow up the calling equipment ...

[geordief]

21 minutes ago, Genady said:

There is a terrorist group on the East Coast preparing a large-scale terrorist attack. When the asteroid hits, they die, among the other millions. Then the call is used and in 2024 they learn about the asteroid and the phone call. They evacuate and change their target so that in 2025, one minute before the call is made, the calling equipment is blown up. The call does not occur. People in 2024 don't know about the coming asteroid hit and don't evacuate. The millions, including the terrorists die. The terrorist attack does not occur. The call is made. People evacuate. Terrorists blow up the calling equipment ...

Groundhog day.Does anyone make any money?

[MigL]

You are not  able to pick and choose circumstances where there are no large scale causality violations with FtL movement or transmissions; the fact remains that if you allow one circumstance of FtL motion/transmission then they are ALL allowed, and causality is gone.
IOW, allowing your example, Moon, also necessarily allows the 'grandfather' paradox or the origin of Romeo and Juliet ( my examples ).

[dimreepr]

15 hours ago, Genady said:

There is a terrorist group on the East Coast preparing a large-scale terrorist attack. When the asteroid hits, they die, among the other millions. Then the call is used and in 2024 they learn about the asteroid and the phone call. They evacuate and change their target so that in 2025, one minute before the call is made, the calling equipment is blown up. The call does not occur. People in 2024 don't know about the coming asteroid hit and don't evacuate. The millions, including the terrorists die. The terrorist attack does not occur. The call is made. People evacuate. Terrorists blow up the calling equipment ...

This reminds me of the film about how Turing cracked the enigma code (can't remember the title), it's not enough to just crack the code, you have to pretend that you haven't.

Causality, in any buggers language, is inevitable; you can't change what you've already done, because that would be a paradox and a paradox is the very definition of impossible. 

If what you say is true, all the terrorist could do is sit and watch the video. 

[studiot]

On 4/10/2023 at 3:30 PM, swansont said:

Causality is a linchpin. Losing it would be a large upheaval.

I agree that causality vitally important.

It is also a very slippery concept to define.

 

On 4/9/2023 at 10:11 PM, MigL said:

This is more usually stated as the 'grandfather paradox', Moon, and yes it does violate causality.

As usually stated, you go back in time and kill your grandfather. 
But then, you were never born to be able to go back in time.
So your grandfather still lives, you are born , and travel back to kill him.
But then you couldn't have ...

 This is the loop Sabine was talking about.

And it doesn't necessarily involve actual travel in time either.
Say you send a manuscript of Shakespeare's \\\romeo and Juliet back to William, who then publishes it, so that you, in the future, can send a copy back to him.
Who actually wrote Romeo and Juliet ?
What exactly 'caused' the play ?

 

Indeed +1

But more than this it emphasises that there is a fundamental difference between space and time.

Nobody thinks that causality is violated because you can travel in space and kill your grandfather.

Modern ideas about paradoxes have led to some interesting connections and the notion of the 'strange loop'.

 

https://en.wikipedia.org/wiki/Strange_loop

https://mathworld.wolfram.com/StrangeLoop.html

[Genady]

8 minutes ago, studiot said:

Nobody thinks that causality is violated because you can travel in space and kill your grandfather.

But if you can travel in space so that you reach Moon in 0.5 s, causality is violated.