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Musings on Time Travel


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Let's start with the Grandfather paradox.
It states: "The grandfather paradox is a paradox of time travel in which inconsistencies emerge through changing the past. The name comes from the paradox's description: a person travels to the past and kills their own grandfather before the conception of their father or mother, which prevents the time traveller's existence. "
Actually, as the traveller has already existed in a timeline, all his actions would do is create a new timeline without him. He would still exist in the new timeline.

Next is thought that if time travel were possible at some point in the future, we would now be inundated with time travellers who travelled back in time from that point on. The fact we see no time travellers tells us at no point in the future does time travel exist.
OK, let me offer a different hypothesis to explain why we see no time travellers.
The future does not yet exist, therefore, you cannot time travel to something which does not exist. This means anyone travelling back in time would find the future they came from does not yet exist, they therefore cannot get back to where they came from. In any case, as with the grandfather paradox, they are now in a different timeline. As soon as the first time travellers did not return home, it would be concluded that time travel was unsafe and impractical, and so would be abandoned. This is why we are not inundated with time travellers.

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But wouldn’t there be a lot of future time travellers who wouldn’t care that they couldn’t return?  Future criminals, for example, might be delighted that they couldn’t be returned to their own time. 

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6 hours ago, Mr Spock said:

Next is thought that if time travel were possible at some point in the future, we would now be inundated with time travellers who travelled back in time from that point on. The fact we see no time travellers tells us at no point in the future does time travel exist.
OK, let me offer a different hypothesis to explain why we see no time travellers.
The future does not yet exist, therefore, you cannot time travel to something which does not exist. This means anyone travelling back in time would find the future they came from does not yet exist, they therefore cannot get back to where they came from. In any case, as with the grandfather paradox, they are now in a different timeline. As soon as the first time travellers did not return home, it would be concluded that time travel was unsafe and impractical, and so would be abandoned. This is why we are not inundated with time travellers.

But wouldn't all the time travellers know about this "issue" of not being able to return anyway? I am pretty sure if they were able to send someone back the "not returning home" conundrum wouldn't have been a surprise or unplanned for....

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Tattoo a date a year in the future on your body. I suggest sole of foot rather than forehead...

Decide in yourself that should time travel be possible in your lifetime you'll come back to that date and tell yourself.

Look forward to this coming date when all will be revealed*

stu

*or not for one of enumerable reasons, but at least you will have a conversation starter for parties (provided you went with the forehead options)

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Seriously though, my thoughts have always been that time travel is only possible within the many worlds/parallel universe theory (at least more possible laws of physics wise).

Since this has it that any and all decisions/changes down to the subatomic level lead to the spawning of another universe, then travel back in our universe would immediate lead to a universe spawning off when you 'landed' at that point in time.

Hence no paradoxes. You are no longer in Kansas Dorithy.

To get back to your original universe, going forward wouldn't work - that'd be forward in the new universe.. you'd need to go back to that branch point and follow the branch of your universe back to the present again.

makes it less fun as nothing you do in the past is 'your' past.. but would still be fun.

I suggest tattooing a date in the future on your forehead.. oh wait.. I've covered that.

 

stu

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On 17/03/2022 at 00:42, Mr Spock said:

The fact we see no time travellers tells us at no point in the future does time travel exist.

... or, perhaps it tells us that a civilisation sufficiently advanced to have developed time travel has also mastered invisibility.

Ponder on that when you next step out of the shower.

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I wonder if "time viewing" might be easier, we can already look back at events in the Cosmos that happened millions of years ago or record something on your phone to watch later. In both cases we cant go back beyond the point where the observer or detector were introduced...yet.

Alan

Edited by Alien 13
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Let's just for moment think about what time travel actually means and what it implies.

Usually when we think about time travel - we simply mean - we "go back" - to yesterday - and everything in world and universe is as it was at some point in time - yesterday.

All atoms, and all particles and everything is at the point it was in that instant. Question is - how do we accomplish that?

There are two obvious ways to do it:

1. We take every particle in the universe and we reposition it so that it is in exact same configuration it was at instant in the past

2. We somehow reverse arrow of time and let universe "rewind" itself to previous state and then we "let it go" again

First approach is obviously impossible

- we simply lack the energy to move each particle to wanted position

- we also lack means of recording each particle position in the universe to be able to reconstruct exact time moment

Second approach implies that there is only one traceable path for particles to move - since we can rewind the universe - which in turn tells us that universe is deterministic - which means there are no parallel timelines and only possible things are perfect time travel loops.

Whenever we go back to the past - we will do exactly the things that will lead us to again some time in the future - go in past again. We won't have option to do otherwise as we live in deterministic universe.

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What an interesting thread.

I personally believe that time travel is impossible, as time itself doesn't actually exist, it's just a perception. What we experience and call time is an illusion created by memory and memory is a function of brain chemistry. Even though we percieve a past, a present and can imagine a future, there is only the present to us. Physics isn't about perceptions, it's about reality. So I don't think there will be any time travellers, though the idea makes for a great Sci-Fi story.

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Yet we still do not have a full description of the meaning of time itself; block time, quantisation of time, even the meaning of "the present" is fraught with ambiguity.  The relationship between time and gravity is one that intrigues me.  Until we have a better understanding of the nature of time then I wonder if we can confidently rule out time travel ! One thing is clear , if it is possible it sure as heck will be taxed :( 

Jim

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well, to be fair forward time travel is perfectly possible. we do it everytime we move.

And given a speed of a decent fraction of C, we'd appreciate it quite meaningfully.

However, the general concensus is that travel BACKWARDS in time is not possible. Except via some worm hole or warp field theories, the first suggesting being crushed to nothing, and the second requiring more energy than their is in the universe.

But, we can dream. As we know, in reality all we need to do is fly around the world quickly*

stu

*ancient movie reference.

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Yes we are travelling forward through or  even travelling "with" time everyday as with every second we age.  As for travelling backward, perhaps we need to be more creative in our thinking.  The door may well be closed to sending matter back in time but what about information !  In our mind we can all envisage a point, often a significant moment in our life, and see and relive that moment in exquisite detail.   A form of time travel perhaps - sure debatable if we are sending information back  but then we have no real idea what consciousness really is  - so perhaps we time travel in our dreams.

Jim 

Edited by saac
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6 minutes ago, Franklin said:

Yes, It's always now.

In the realm of special relativity it really does not exist. No sooner than you have named it it becomes the past and agreeing on "it" by observers in different frames of reference is headachingly impossible !  The notion of "the present"  is further complicated by the interplay of simultaneity.

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

Jim 

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2 minutes ago, saac said:

No sooner than you have named it it becomes the past and agreeing on "it" by observers in different frames of reference is headachingly impossible !

It's a bit of a mind bender.

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9 minutes ago, Franklin said:

It's a bit of a mind bender.

I long gave up trying to understand it. Maybe sometime in the past I will get it :) 

Jim 

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18 hours ago, iantaylor2uk said:

If you are a photon, time does not exist

Can a photon exist without time ?

 

To exist you would have to have a period of time to exist in.

There a Photon cannot exist...QED...

Edited by Kev M
typo
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3 minutes ago, Kev M said:

Can a photon exist without time ?

 

To exist you would have to have a period of time to exist in.

There a Photon cannot exist...QED.

hey everything just went dark ; where am I.  Thanos have you clicked your fingers again :) 

Jim 

Edited by saac
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I suppose time travel is dependent on how much we know about Maths/Physics etc, if we think we already know 50% of everything that is knowable then time travel is impossible, if however as I believe our knowledge is less than 0.0000000000000000000000000001 % as I suspect then anything is possible.

Alan

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4 minutes ago, Mr Spock said:

There's no such thing as the present. Time is constantly moving forward so everything we perceive is in the past.

That’s exactly what I said next week.

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