Just curious. It's an interesting topic.

Time travel to the past, no.

Forward is easy though. Just wait for it

Most forms of time travel, i.e. the ones portrayed in science fiction, are ruled out by physics.

Time travellers only attended Stephen Hawking's party because they knew they could trust him to keep quiet and not destroy the delusion of causality.

Forward Time travel as per the "twin Paradox"  is allowed for and theoretically possible according to relativity. Backward time travel is another matter altogether.

But Kip explains it better then I. 

https://plus.maths.org/content/time-travel-allowed

Time travel to the past would mean there are two or more the same particles existing simultaneously..

e.g. you imaginary travel to past 1h, and there are two copies of you and you+1h..

Particle is in two places at the same 'time'..

 

 

Edited January 8, 20188 yr by Sensei

It's out of fashion these days, but I'm not aware of any reason that an antiparticle can't be interpreted as a particle travelling backwards in time as in e.g. Feynman diagrams.

The 'same' particle exists in two places at the same time.

 

On 08/01/2018 at 2:56 PM, Sensei said:

Time travel to the past would mean there are two or more the same particles existing simultaneously..

e.g. you imaginary travel to past 1h, and there are two copies of you and you+1h..

Particle is in two places at the same 'time'..

It wouldn't be the past, either. Right now, there is just me in this room. If I step into  a time machine in an hours time and go back an hour, there will be two of us. That's obviously not THE past. It's something that looks similar but is different.

Even if I replaced the version of me that was there an hour ago, it's still not the past. It's similar, but my brain and body is an hour older. I might have had a pee or poo, or a meal, so my weight wouldn't be the same. So the act of going into the past means it's NOT the past. 

I would say that it's not theoretically impossible to observe the past. That's what we do when we look through a telescope. Maybe it would be possible one day to look at reflections of the past on Earth, bouncing off far away bodies. Highly unlikely though. There's more chance of us being sent pictures or video of our past by aliens on far away planets. No sign of it yet though. 

On 12/31/2017 at 7:07 PM, MegaDestructor said:

Just curious. It's an interesting topic.

If by discovered you mean realized to be hypothetically possible then yes, https://en.wikipedia.org/wiki/Tipler_cylinder 

But if you mean likely to happen and or has it been used, no. 

7 hours ago, mistermack said:

It wouldn't be the past, either. Right now, there is just me in this room. If I step into  a time machine in an hours time and go back an hour, there will be two of us. That's obviously not THE past. It's something that looks similar but is different.

Even if I replaced the version of me that was there an hour ago, it's still not the past. It's similar, but my brain and body is an hour older. I might have had a pee or poo, or a meal, so my weight wouldn't be the same. So the act of going into the past means it's NOT the past.

Might be able to meet yourself, then go on to become the future self you meet.

I suspect Universe doesn't really allow time travel backwards though.