Musings on Time Travel

[Kev M]

Time can only travel in one direction....the paradoxes raised would make this obvious.

Anything that "stands still in time" by definition cannot exist.

Our understanding of the universe seems insufficient to deal with things like photons and their relationship with time ( or spacetime).

We are missing something.....

 

 

 

 

 

 

 

[Kev M]

11 hours 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 a tricky concept......

Would the moment of perception not be in the present ?

Even if that which was perceived was in the past ( which you are correct it would always have to be ).

[iantaylor2uk]

11 minutes ago, Kev M said:

Time can only travel in one direction....the paradoxes raised would make this obvious.

Anything that "stands still in time" by definition cannot exist.

Our understanding of the universe seems insufficient to deal with things like photons and their relationship with time ( or spacetime).

We are missing something.....

 

 

 

 

 

 

 

Physicists understand plenty about photons. Relativity shows that objects can travel through space and time, but if a particle travels at the speed of light (and only massless particles can) then those particles don't travel through time at all. So time stands still for photons, but they definitely exist.

[Toltec]

39 minutes ago, iantaylor2uk said:

Physicists understand plenty about photons. Relativity shows that objects can travel through space and time, but if a particle travels at the speed of light (and only massless particles can) then those particles don't travel through time at all. So time stands still for photons, but they definitely exist.

This is precisely one of the things I love about observartional astronomy, that photon from a distant star that excited the photosensitive molecule in your eye just connected you to that star instantaneously.

On time travel, something which has been covered in various books and films is that the moment of conception is so tightly bound to the moment and circumstances that the tinest change by a time traveller would result in a number of people never being born.

[Marvin Jenkins]

Reminds me of that Red Dwarf episode where they get hold of a time machine.

All expectations are to go back in time and get back to Earth…. Bang, it happens but they are still in the same physical place in the universe.

Marv

[Olsin]

I was going to tell you all a good joke about time travel but it turned out nobody liked it..

Apparently 7% of everything we think we know will be proven to be incorrect or in need of some adjustment within a 5 year period. So with a start point at 2022, by 2027, 7% of what we think we know today will incorrect. By 2032, 14% of 2022 knowledge will be incorrect, 2037 = 21% incorrect. Carrying that out suggests that sometime between 2092 and 2097, 100% of all we think we know today will be shown to incorrect.
Is time travel into the future possible .. maybe.
Is time travel into the past possible .. maybe.

Why don't we see time travelers?

If they have the technology to travel through a medium that we don't even know what is, then what other kinds of tech do they have? could that tech help them remain undetectable? Does time travel only permit travel in non corporeal form or a phase shifted form or some other form we can't see/interact with or don't recognize?
Will we discover we have to change our physiology or create via genetic engineering creatures especially designed to be able to time travel and use them to collect data in the same way we send probes and rovers to the planets and moons of our own solar system or crush resistant vessels to the depths of the oceans? Would we recognize these devices if they were designed by future minds using future tech to not be discovered?

Maybe, maybe, maybe.....

One thing is certain, the future a thousand years from now won't resemble today much and the future 2 thousand years from now won't resemble the future a thousand years from now much.
Truth is transient and i bet there's many more paradigm shifts waiting out in the future as have ever unfolded in the past. How many of them will  end up completely changing our social and technological direction?

What is almost unimaginable/incomprehensible today may be abc for a 1st year secondary school pupil in a dozen generations from now..

 

Edited March 25, 2022 by Olsin

[Kev M]

22 hours ago, iantaylor2uk said:

Physicists understand plenty about photons. Relativity shows that objects can travel through space and time, but if a particle travels at the speed of light (and only massless particles can) then those particles don't travel through time at all. So time stands still for photons, but they definitely exist.

I get the gist of what you are saying but it raises other issues around definitions as well.

For something to "exist" it has to "pass through" at least 2 moments in time ( debates around whether time is continuous or discrete does not matter in this case ).

 

By definition a "point particle" can not exist either.....a particle has to have dimension otherwise it is not a particle.....calling something a "point particle" is nonsense.

How can the position of a "point particle" be defined if it has no dimensions, how can it interact with anything if it cant "touch" anything

It can be called a waveform ( or similar ) and it can then possibly do these things but then it is not a "point particle".

 

 

And just to emphasise my points about nonsense.....

We cannot accurately measure the speed of light as we do not have a suitable "tape measure".

 

Consider the following....

We have decided we should all adopt the our individual Right Hand ( or your local speed of light) as the standard unit of measurement...

Measure your Right Hand (or your local speed of light) and see if it is the the same size as your standard unit of measurement.....

That's the problem....

 

 

[iantaylor2uk]

You clearly have no understanding of modern physics. Firstly, particles interact via fields, not through "touch". Electric and magnetic field are everywhere and interact in this way. Secondly, the position of particles is not known precisely due to the uncertainty principle. Particles under certain circumstances act as point particles and under other circumstances as waves. Thirdly, it is experimentally obvious that photons do exist. I don't know where you got your definition of existence from, but photons can be created and destroyed, and time obviously passes for observers of the photons but time stands still for the photons themselves. 

[Kev M]

On 26/03/2022 at 09:12, iantaylor2uk said:

 Firstly, particles interact via fields, not through "touch". Electric and magnetic field are everywhere and interact in this way. 

The magnetic fields "touch" or interact in various ways....."touch" was easier to type.

 

On 26/03/2022 at 09:12, iantaylor2uk said:

Particles under certain circumstances act as point particles and under other circumstances as waves. 

"act as"..... so they are not actually point particles then ?

 

On 26/03/2022 at 09:12, iantaylor2uk said:

 Thirdly, it is experimentally obvious that photons do exist. I don't know where you got your definition of existence from, but photons can be created and destroyed, and time obviously passes for observers of the photons

Yep, generally agree with that.

 

On 26/03/2022 at 09:12, iantaylor2uk said:

 but time stands still for the photons themselves. 

That's the bit I have difficulty with.....and have still to find anything that proves this....plenty of statements but no proof.

If you could educate me on this it would be appreciated.

 

 

[wulfrun]

@Kev M I suggest reading the derivation for E = mc², it will lead you to the proof. Any particle with no mass* is forced to travel at the speed of light and does not experience time. I can suggest a good book, "Why Does E = mc²?"by Geoff Forshaw (Foreshaw?)/Brian Cox. It's reasonably non-mathematical but fairly intensive.

*technically, rest-mass not just "mass".

As for point-particles, I think the word "particles" is a bit misleading. It conjures up the idea of (say) tiny billiard-balls or some such, which is wrong because they couldn't be zero size. Just consider them as "things", with measurable properties.

 

Edited March 27, 2022 by wulfrun
typo

[saac]

1 hour ago, Kev M said:

That's the bit I have difficulty with.....and have still to find anything that proves this....plenty of statements but no proof.

If you could educate me on this it would be appreciated.

 

 

It is a relativistic effect and not absolute. To an observer in an inertial frame of reference  (observer on Earth)  the photon's journey certainly takes a discrete amount of time.  As for what the photon experiences well we need to be careful here as photons of course experience nothing.  The oft quoted comment that they experience no time is a consequence of the description of time dilation given by  t' = t * Lorentz Factor , where t' is the dilated time and t the proper time.  Imbuing photons and particles with the ability to "experience" can be problematic if taken out of context. 

Jim 

Edited March 27, 2022 by saac

[saac]

I'm intrigued by the thought that somebody raised earlier  in effect linking time to the position  of all other particles in the universe (presumably also the disposition of all field fluctuations as well). I had never thought of time like that but the idea does have an appeal.  On first thought it may raise the possibility that in a very localised domain time could be reversed. The domain would need to be isolated from all other influence in the remainder of the universe . No doubt the action to reorder all positions and other influences would need to be done in a manner again isolated from the rest of the universe - so yes a difficulty right there . We ain't going to be doing that anytime soon: unless we already have     

Jim 

 

ps - I wonder if this has any linkage to the Block Universe theory and block time. 

Edited March 27, 2022 by saac

[vlaiv]

On 25/03/2022 at 21:31, Olsin said:

Apparently 7% of everything we think we know will be proven to be incorrect or in need of some adjustment within a 5 year period. So with a start point at 2022, by 2027, 7% of what we think we know today will incorrect. By 2032, 14% of 2022 knowledge will be incorrect, 2037 = 21% incorrect. Carrying that out suggests that sometime between 2092 and 2097, 100% of all we think we know today will be shown to incorrect.

I'm not really comfortable with this assertion.

Can you point out things that are proven incorrect in past 5 years? I certainly feel that out of volume of my knowledge - 7% was not proven to be wrong.

 

[vlaiv]

1 minute ago, saac said:

I'm intrigued by the thought that somebody raised earlier  in effect linking time to the position  of all particles (presumably also the disposition of all field fluctuations as well). I had never thought of time like that but the idea does have an appeal.  On first thought it may raise the possibility that in a very localised domain time could be reversed. The domain would need to be isolated from all other influence in the remainder of the universe . No doubt the action to reorder all positions and other influences would need to be done in a manner again isolated from the rest of the universe - so yes a difficulty right there . We ain't going to be doing that anytime soon: unless we already have     

Jim 

Laws of physics on tiniest scales simply don't have preference for direction of time.

Formulae and laws work same if you introduce certain symmetries.

Look at CPT symmetry  - if you reverse charge, parity and time - everything still works as it should.

 

 

[saac]

28 minutes ago, vlaiv said:

Laws of physics on tiniest scales simply don't have preference for direction of time.

Formulae and laws work same if you introduce certain symmetries.

Look at CPT symmetry  - if you reverse charge, parity and time - everything still works as it should.

 

 

They do of course vlaiv but if we are to "time travel" we in the classical domain would be subject to general relativity where time is fluid.  Maybe that is the answer, maybe we need do as Ant Man did and build a Quantum  machine  - he used it to evade the blip when Thanos clicked his fingers (sorry my geek side running riot here)  

Jim

checking out CPT symmetry now, thanks for hint.

Edited March 27, 2022 by saac

[vlaiv]

47 minutes ago, saac said:

They do of course vlaiv but if we are to "time travel" we in the classical domain would be subject to general relativity where time is fluid.  Maybe that is the answer, maybe we need do as Ant Man did and build a Quantum  machine  - he used it to evade the blip when Thanos clicked his fingers (sorry my geek side running riot here)  

Jim

checking out CPT symmetry now, thanks for hint.

Well - I did try to point out one of issues with time travel.

Fact that time is "fluid" in GR/SR just points to the fact that time is nothing more than "rate" of interactions.

We seem to often think in terms of "monolithic" time - as in "time waits for no man" - it "flows" whether there is something present or not.

I don't think that is true - for one thing - there is always something present even if "nothing" is there - quantum fields are omni present and fluctuations in those fields represent passage of time.

We can pose following question - if we have stationary system - empty or not, it does not matter - if we can imagine some sort of "spherical particles" suspended in space that don't move with respect to one another - no gravity, just like "frozen" image - frozen in time.

Does time flow for such system? If it does - how long has such system been like that? There is no way to tell - no way to indicate passage of time (unless we stand outside of that system with a clock that moves - so there must be something interacting / moving in order for time as something meaningful to exist).

If we accept that time is merely rate of interactions in the system - the fluidity of time is nothing special - we don't interact the same with stationary things and moving things, so rate of interaction is not necessarily the same.

Given that time is just rate of interaction and one more thing - there must be ordered set of sorts. We know what came before / after - regardless of direction - there is sequence of events - that follow in order.

Given those two things - we can see that what we think of "time travel" is just - resetting system to some previous configuration. Either by reversing order of things - CPT symmetry thing - we reverse charge of every particle in universe, we inverse momentum of each particle in universe and we inverse parity - and whole universe will start running in reverse - when we "reach" wanted point - we flip CPT again.

In order for that to happen - we must be able to somehow:

1. exclude ourselves from the universe and its laws

2. flip CPT switch at our discretion (don't even want to know what sort of energy would be needed for reversal of all momenta)

Another thing is of course to "rearrange" all the particles in universe in configuration that they were in at wanted point in time - that again requires:

1. us being able to exclude ourselves from the rest of universe

2. have a blue print of what the universe was like at wanted time - all the particles with their positions and momenta

3. have enormous energy to rearrange current state of universe to that state.

In either of these - we would need mechanism to remove old selves from the universe and replace with current selves that were outside of the universe when flip happened.

Type two with non deterministic universe allows for "time lines / time branches".

[saac]

3 minutes ago, vlaiv said:

Well - I did try to point out one of issues with time travel.

Fact that time is "fluid" in GR/SR just points to the fact that time is nothing more than "rate" of interactions.

We seem to often think in terms of "monolithic" time - as in "time waits for no man" - it "flows" whether there is something present or not.

I don't think that is true - for one thing - there is always something present even if "nothing" is there - quantum fields are omni present and fluctuations in those fields represent passage of time.

We can pose following question - if we have stationary system - empty or not, it does not matter - if we can imagine some sort of "spherical particles" suspended in space that don't move with respect to one another - no gravity, just like "frozen" image - frozen in time.

Does time flow for such system? If it does - how long has such system been like that? There is no way to tell - no way to indicate passage of time (unless we stand outside of that system with a clock that moves - so there must be something interacting / moving in order for time as something meaningful to exist).

If we accept that time is merely rate of interactions in the system - the fluidity of time is nothing special - we don't interact the same with stationary things and moving things, so rate of interaction is not necessarily the same.

Given that time is just rate of interaction and one more thing - there must be ordered set of sorts. We know what came before / after - regardless of direction - there is sequence of events - that follow in order.

Given those two things - we can see that what we think of "time travel" is just - resetting system to some previous configuration. Either by reversing order of things - CPT symmetry thing - we reverse charge of every particle in universe, we inverse momentum of each particle in universe and we inverse parity - and whole universe will start running in reverse - when we "reach" wanted point - we flip CPT again.

In order for that to happen - we must be able to somehow:

1. exclude ourselves from the universe and its laws

2. flip CPT switch at our discretion (don't even want to know what sort of energy would be needed for reversal of all momenta)

Another thing is of course to "rearrange" all the particles in universe in configuration that they were in at wanted point in time - that again requires:

1. us being able to exclude ourselves from the rest of universe

2. have a blue print of what the universe was like at wanted time - all the particles with their positions and momenta

3. have enormous energy to rearrange current state of universe to that state.

In either of these - we would need mechanism to remove old selves from the universe and replace with current selves that were outside of the universe when flip happened.

Type two with non deterministic universe allows for "time lines / time branches".

Even accepting that we could  measure and document the whole universe and then reorder it to a previous state, the moment we introduce ourselves to that new state (the point of our endeavour) we no longer have a universe in the state (point in time we sought) - we have contaminated it by our presence !  Such a practice would  also preclude concurrent time travel by two or more independent actors.   So for that reason I'm not investing in any time travel proposal yet - I never was an early adopter  

Jim 

[iapa]

It's, supposedly, an infinite universe.

Basing everything on that premise, everything is possible, so, somewhere, in somewhen, time travel is possible.

There is also consideration needed to parallel, multiple separate, and bubble universes.

It's there, we just don't know about it yet.

For me, I would hate o revisit my past, memories are bad enough. The future is dependent on my actions - which I rarely take consideration of

 

[Alien 13]

Maybe there is another way to time travel, I often re visit the past in my dreams but there are errors, now if we could link lots (think billions) of minds together to fill in the missing gaps then....

Alan

[Kev M]

2 hours ago, wulfrun said:

 E = mc², it will lead you to the proof. Any particle with no mass* is forced to travel at the speed of light and does not experience time.

So if m=0 then E=0

Therefore photons have no energy.....that cant be right.... or can it ?

 

2 hours ago, wulfrun said:

As for point-particles, I think the word "particles" is a bit misleading. It conjures up the idea of (say) tiny billiard-balls or some such, which is wrong because they couldn't be zero size. Just consider them as "things", with measurable properties.

Exactly my point, agree on this.

[Kev M]

22 minutes ago, iapa said:

It's, supposedly, an infinite universe.

Basing everything on that premise, everything is possible..............

Indeed if the universe was infinite, then not only is everything possible but everything actually happens....an infinite amount of time each.

Obviously the universe cannot be infinite.

[wulfrun]

9 minutes ago, Kev M said:

So if m=0 then E=0

Therefore photons have no energy.....that cant be right.... or can it ?

No, as pointed out "rest mass". If it were possible stop a photon (without thus destroying it) and weigh it, you'd find it weighed nothing whatsoever, nada, zero. Because energy and mass are "the same thing" though, the photon has an equivalent mass due to its energy.

[saac]

32 minutes ago, Kev M said:

So if m=0 then E=0

Therefore photons have no energy.....that cant be right.... or can it ?

 

Exactly my point, agree on this.

No that equation (which is incomplete)  just shows the  equivalence  of mass and energy it would be an incorrect conclusion to say that it points to photons have no energy.  The energy of a photon is directly proportional to its frequency.

Jim  

[saac]

30 minutes ago, Kev M said:

Indeed if the universe was infinite, then not only is everything possible but everything actually happens....an infinite amount of time each.

Obviously the universe cannot be infinite.

Why?   Actually no, only joking we have a separate whole thread on that already   

Jim 

[saac]

44 minutes ago, Alien 13 said:

Maybe there is another way to time travel, I often re visit the past in my dreams but there are errors, now if we could link lots (think billions) of minds together to fill in the missing gaps then....

Alan

Exactly Allan, I think time travel is permissible  within our consciousness only. We are not sending anything back, not violating any laws and the experience can at times be very real.

Jim 

Edited March 27, 2022 by saac