Does Lorentz invariance rule out time travel to the past?

[John Fennie]

Is going back in time fundamentally ruled out by Lorentz invariance? Or not? Or is it something else?

 

[Nugatory]

What exactly do you mean by "going back in time"?

 

[John Fennie]

What exactly do you mean by "going back in time"?

Either as a physical transportation, or literally turning back time.

 

[ZapperZ]

Either as a physical transportation, or literally turning back time.

Try it. Substitute t → -t in any of the Lorentz transformation. Has anything changed?

Zz.

 

[John Fennie]

Try it. Substitute t → -t in any of the Lorentz transformation. Has anything changed?

Zz.

Take t to be positive, the metric will then have all positive (or all negative) components, hence no time component.
But I am not sure what you are trying to have me see.

 

[jbriggs444]

But I am not sure what you are trying to have me see.

The t term in the metric is squared. Negating its sign has what effect?

 

[John Fennie]

The t term in the metric is squared. Negating its sign has what effect?

It does not have any effect on the spacetime interval, which means that having negative t is allowed.

 

[sophiecentaur]

which means that having negative t is allowed.

Do you believe that all possible mathematical solutions apply to the real Universe?
You should, perhaps replace "means" with "could imply".

 

[John Fennie]

Do you believe that all possible mathematical solutions apply to the real Universe?
You should, perhaps replace "means" with "could imply".

I understand. How do you guys interpret time physically? Because even time reversal is allowed, how can one physically have say, a particle, go back in time? Is there any sort of theory on the physical applications for going backward? (Just like traveling in a spaceship is a physical application for going forward.)

 

[Drakkith]

How do you guys interpret time physically?

That which a clock measures.

Because even time reversal is allowed, how can one physically have say, a particle, go back in time? Is there any sort of theory on the physical applications for going backward? (Just like traveling in a spaceship is a physical application for going forward.)

There are no accepted theories that unambiguously accept or suggest that time travel into the past is a real possibility.

Note that discussion of time travel into the past is generally not allowed here at PF.

Thread locked.