Time Travel: Setup & Challenges for Safe & Accurate Travel

[ForTheLoveOfPhysics]

I like time travel for entertainment purposes in books/movies but there’s one fundamental flaw I haven’t seen discussed.

Any time travel example without the use of a ‘gate’ or wormhole (Star Gate SG1 for example) focuses on time only. The problem with these is you need to firstly travel in time or space to ‘setup’ the other end.

However as earth moves through space around the Sun, Milky way galaxy and towards the Great Attractor at hundreds of thousands of kilometres per second; travelling in time for a fraction of a second would have you left out in space.

So I’m order to truely time travel it must be time/space travel.

The only way I can see this being counteracted is to get yourself and your ‘device’ into orbit around earth first and then once you reach your desired time come back to earth.

The ‘device’ would have to travel through time linearly (either direction) vs ‘suddenly’ disappearing in one time and arriving in another.

Maybe some anti-matter in dense and massive enough quantities could be used for travelling backwards in time, and matter used for travelling forward (Similar to travelling close to a Black Hole.)

I imagine the first person to invent time travel finding themselves suddenly in space with their blood boiling and heads exploding. Would make a comical short?!

 

[phinds]

Since time travel itself is fiction, why worry about adding another fiction to that fiction? Since if it has time travel, you've already given up on science, It's the story that matters.

 

[ForTheLoveOfPhysics]

Since time travel itself is fiction, why worry about adding another fiction to that fiction? Since if it has time travel, you've already given up on science, It's the story that matters.

Fair point!

Although time travel isn’t technically fiction if you take into account relativity. Like in that documentary Interstellar haha

 

[Algr]

It's been thought of before.
The H.G. Wells time machine retains physical contact with Earth while time traveling, and thus can be expected to stay with it. The TARDIS actually has "dimensions in space" as part of its name, and can travel through space with or without time travel. In the first episode they mention time as the fourth dimension and something mysterious as the fifth. Star Trek time travel involves the gravity of a star, and so can be expected to take the starship to wherever the star was in the past. And Quantum Leap .... whatever. You get the idea.

 

[Trysse]

There is a book by Joe Haldeman, The Accidental Time Machine, which somehow takes the spatial movement into account. However, in the book this does not take the time traveller into space. Just somewhere else on earth.

 

[jack action]

However as earth moves through space

How would one know? Doesn't it all depend on what is chosen as a frame of reference? Am I revolving around the center of the Earth or is the center of the Earth revolving around me?

With the correct perspective applied, everything could move with respect to the time machine which is at point (0, 0, 0, 0). Then the time machine moves only along the time dimension. Planets and galaxies will be at different places when it "arrives" at the destination, but it will still be at the same contact point on Earth. One hopes it wasn't (or won't be) a flooded area!

 

[pbuk]

With the correct perspective applied, everything could move with respect to the time machine which is at point (0, 0, 0, 0).

Yes: this effect is documented in the literature (e.g. Wells, 1895) and is illustrated to great effect in the authoritative 1960 film The Time Machine.

1. Wells, Herbert George (1895). The Time Machine. London: William Heinemann.

 

[DrClaude]

The H.G. Wells time machine retains physical contact with Earth while time traveling, and thus can be expected to stay with it

Yes: this effect is documented in the literature (e.g. Wells, 1895) and is illustrated to great effect in the authoritative 1960 film The Time Machine.

1. Wells, Herbert George (1895). The Time Machine. London: William Heinemann.

There is an inconsistency in The Time Machine that has always bothered me. When first presenting the prototype, the machine completely disappears to those present as it travels to the future. But when the time traveller is in the machine, he sees the outside world change in a "fast forward" way (more akin to relativity of time). People outside the time machine should thus still see the machine, as it travels.

 

[pbuk]

Sorry @Algr, I didn't see your reference. @DrClaude I was also once bothered by this but then I realised that the machine works by generating a local anisotropy in the one-way speed of light

 

[Vanadium 50]

There is an inconsistency in The Time Machine

I think this was covered in the book

The idea is that if you are going through time 100x faster, you have 1/100 the impact on your surroundings. And so forth. The context is that the onlookers are debating whether the small prototype went into the past or the future.

 

[DrClaude]

I think this was covered in the book

The idea is that if you are going through time 100x faster, you have 1/100 the impact on your surroundings. And so forth. The context is that the onlookers are debating whether the small prototype went into the past or the future.

Yes, but there is still an asymmetry that bothers me.

 

[Vanadium 50]

I see it as symmetric.

Why, when riding in the machine, are you not blinded by a century's worth of light smacking into your eyeballs every second? Because the outside world has only 1/x of its normal impact on you. Why are you intangible and invisible? Because you have only 1/X of the impact on the outside world.

 

[bob012345]

There is an inconsistency in The Time Machine that has always bothered me. When first presenting the prototype, the machine completely disappears to those present as it travels to the future. But when the time traveller is in the machine, he sees the outside world change in a "fast forward" way (more akin to relativity of time). People outside the time machine should thus still see the machine, as it travels.

That doesn't seem inconsistent to me. People outside could in principle see the machine pass through their time but it would generally be moving at such a rate they probably wouldn't notice it.

 

[DaveC426913]

However as earth moves through space around the Sun, Milky way galaxy and towards the Great Attractor at hundreds of thousands of kilometres per second; travelling in time for a fraction of a second would have you left out in space.

Not unless your time machine has some ability to know its location in some (non-existent) absolute spatial frame of reference.

It might be simplest to just assume that, despite moving in time, it is not free of the effects of gravity and inertia. Even as it travels in time, it is still held to the Earth's surface by gravity, so why would it go anywhere physically?

 

[DaveC426913]

That doesn't seem inconsistent to me. People outside could in principle see the machine pass through their time but it would generally be moving at such a rate they probably wouldn't notice it.

But what would "passing through their time" look like?
You walk in to the room and the time machine is there (because it passed through time in this room five minutes ago, and five seconds ago and now), and its still there when you leave (because it's passing through time five seconds from now and five minutes from now.)

Imagine it from the traveller's POV. You see the sun come up, the someone zooms into the room, zooms around and zooms out again. In other words, from the outside POV, the time machine was there the entire time.

 

[jack action]

In other words, from the outside POV, the time machine was there the entire time.

Imagine a 3D space instead of a 4D space-time. I want to move along the z-axis while staying the same (x,y) line. People in my initial (x,y, z₀) plane don't see me in their plane once I begin moving.

Why would it be different when I move along the time axis, leaving my initial (x,y,z,t₀) space?

 

[bob012345]

But what would "passing through their time" look like?
You walk in to the room and the time machine is there (because it passed through time in this room five minutes ago, and five seconds ago and now), and its still there when you leave (because it's passing through time five seconds from now and five minutes from now.)

Imagine it from the traveller's POV. You see the sun come up, the someone zooms into the room, zooms around and zooms out again. In other words, from the outside POV, the time machine was there the entire time.

But you, the time traveller see all times in sequence. But to the person fixed in time, whenever you observe, the machine has already been there and gone. I think.

 

[DaveC426913]

Imagine a 3D space instead of a 4D space-time. I want to move along the z-axis while staying the same (x,y) line. People in my initial (x,y, z₀) plane don't see me in their plane once I begin moving.

Why would it be different when I move along the time axis, leaving my initial (x,y,z,t₀) space?

Unless the observers are also moving along the z-axis (because it's time).

 

[jack action]

Unless the observers are also moving along the z-axis (because it's time).

Yes but - as mentioned in post #17 by @bob012345 - you are always moving faster than them. (Otherwise, you wouldn't be time-traveling.) They will "see" you again only if you slow down and let them catch up on you. At that point, you have to keep your time-traveling speed the same as theirs to be able to interact with them.

Imagine being in an elevator moving up with other people and then jumping on a faster elevator. You will all pass through the same elevation but never at the same time.

 

[pinball1970]

There is an inconsistency in The Time Machine that has always bothered me. When first presenting the prototype, the machine completely disappears to those present as it travels to the future. But when the time traveller is in the machine, he sees the outside world change in a "fast forward" way (more akin to relativity of time). People outside the time machine should thus still see the machine, as it travels.

The machine is not actually moving in space at all so how is it "traveling?"
In fact it did not make sense at all, to travel forward in time he would have to move at significant velocity
To go backwards in time (did he actually do that?) he would have to go faster than C.
Both involve moving in space.
EDIT. How would represent it in terms of Minkowski?

 

[Vanadium 50]

(1) The book predates relativity by a decade.
(2) The 1960 movie is set 5 years before relativity.
(3) There is no need to guess at what internal or external observers might see and why, because its right there in the book.

The best you can say is "Harumph! That's not how I think a time machine should work!" and "what does this HG Wells character know about writing anyway!"

I suppose.

 

[jack action]

The machine is not actually moving in space at all so how is it "traveling?"

He's time-traveling (t), so he can remain fixed in space (x,y,z) in the four-dimensional spacetime (x,y,z,t).

To go backwards in time (did he actually do that?) he would have to go faster than C.

Other people are also constantly moving along the axis of time. If you go faster than them on that axis, you're ahead. If you slow down along that axis, they will catch up.

 

[Malapine]

(1) The book predates relativity by a decade.
(2) The 1960 movie is set 5 years before relativity.
(3) There is no need to guess at what internal or external observers might see and why, because its right there in the book

(4) The Time Machine is just a framing device for social commentary on inequality between workers and aristocrats and does not need to be physically rigorous.

 

[bob012345]

He's time-traveling (t), so he can remain fixed in space (x,y,z) in the four-dimensional spacetime (x,y,z,t).

Other people are also constantly moving along the axis of time. If you go faster than them on that axis, you're ahead. If you slow down along that axis, they will catch up.

We are all space-time travelling even at the rate of 1 sec/sec because the earth moves. But we can assume the time traveller also moves with the earth as necessary, they are where-ever the earth is whenever they are there just as we are all on the surface of the earth moving with that surface. It seems reasonable to assume such a similar effect for the story. If not then think of the machine as creating an instantaneous portal to the same place in a stream of different times.

 

[Vanadium 50]

Physically rigorous? There are no Time Machines!

As far as social commentary, who are Wells' good guys? The parasitic Eloi, or the Morlocks who prey on them?

 

[DaveC426913]

As far as social commentary, who are Wells' good guys? The parasitic Eloi, or the Morlocks who prey on them?

It was a cautionary tale - warning of the ultimate outcome from social divergence of the white collar versus blue collar classes.

 

[pinball1970]

Physically rigorous? There are no Time Machines!

As far as social commentary, who are Wells' good guys? The parasitic Eloi, or the Morlocks who prey on them?

I did not wander into the relatively forum by mistake again did I?

Re time machines. Yes there are, legs, cars, planes and rockets. Future only of course and only v very small differences.

In terms of biological rigour with the Eloi and Morlocks, I like fact the underground environment, provided evolutionary pressure towards lack of pigmentation. No issue there.
In terms of food source there is always the risk of zoonotic events with mammals and pathogen similarity.
100s of 1000s of years of evolution would reduce that risk but if bats, badgers and bulls can mess us up then no reason an Eloi would not kuru the hell out of those Morlocks.
EDIT:If no issues there then a mutualistic symbiotic system is not that crazy. Reminded me of the ant aphid thing.

 

[pinball1970]

He's time-traveling (t), so he can remain fixed in space (x,y,z) in the four-dimensional spacetime (x,y,z,t).

Other people are also constantly moving along the axis of time. If you go faster than them on that axis, you're ahead. If you slow down along that axis, they will catch up.

Thanks

 

[pinball1970]

Sometimes it's good to look at a sci concept from yester year and apply a modern take. It's fun.

 

[L Drago]

I like time travel for entertainment purposes in books/movies but there’s one fundamental flaw I haven’t seen discussed.

Any time travel example without the use of a ‘gate’ or wormhole (Star Gate SG1 for example) focuses on time only. The problem with these is you need to firstly travel in time or space to ‘setup’ the other end.

However as earth moves through space around the Sun, Milky way galaxy and towards the Great Attractor at hundreds of thousands of kilometres per second; travelling in time for a fraction of a second would have you left out in space.

So I’m order to truely time travel it must be time/space travel.

The only way I can see this being counteracted is to get yourself and your ‘device’ into orbit around earth first and then once you reach your desired time come back to earth.

The ‘device’ would have to travel through time linearly (either direction) vs ‘suddenly’ disappearing in one time and arriving in another.

Maybe some anti-matter in dense and massive enough quantities could be used for travelling backwards in time, and matter used for travelling forward (Similar to travelling close to a Black Hole.)

I imagine the first person to invent time travel finding themselves suddenly in space with their blood boiling and heads exploding. Would make a comical short?!

Time travel to future is theoretically possible and practical also although difficult.


According to Einstein's time dilation, dilated time = actual time / power root of 1- (square of velocity /speed of light). The faster we go, the slower time goes for us. If we will be able to travel in incredibly high say 80 percent speed of light which is not possible according to current technology time would pass slowly for us and when we finally stop and return to earth, we will be in future.

According to Einstein's general relativity. The more the mass, the more the gravity and more the curvature of space time and slower the time. So if we could find and go to a planet with considerably large amount of gravitational field than earth. Stay there for sometime and return, then we will be in future.

But time travel to past is not possible according to Einstein's general and special relativity.

 

[PeroK]

But time travel to past is not possible according to Einstein's general and special relativity.

This is not true. There is the concept of closed timelike curves (CTCs):

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

Whether these exotic solutions of the Einstein Field Equations are physically possible is another question. But, the theory permits them.

 

[L Drago]

This is not true. There is the concept of closed timelike curves (CTCs):

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

Whether these exotic solutions of the Einstein Field Equations are physically possible is another question. But, the theory permits them.

As it is physically not possible, even if we could develop a technology somehow to travel in 90-99 percent speed of light, we will be in future but won't be able to return.

 

[PeroK]

As it is physically not possible, even if we could develop a technology somehow to travel in 90-99 percent speed of light, we will be in future but won't be able to return.

I'm not sure what you mean by that. It's physically possible to undertake a journey from Earth at sufficient relative speed that the differential ageing between the spacecraft and the Earth is significant. Whether human civilization ever achieves this capability is an open question.

 

[L Drago]

I'm not sure what you mean by that. It's physically possible to undertake a journey from Earth at sufficient relative speed that the differential ageing between the spacecraft and the Earth is significant. Whether human civilization ever achieves this capability is an open question.

I am telling it is not physically possible for CTCs to exist probably. You can correct me if I am wrong.

 

[phinds]

The faster we go, the slower time goes for us.

time would pass slowly for us

I'm not clear on whether you are just using shorthand for what actually happens or if you mistakenly believe that time actually does slow down for a traveler. Just to be clear, it does not. The traveler's clock ticks away at the exact same one second per second as the stay at home's clock.

If you do not understand this concept of proper time, then you are making the common mistake of confusing time dilation with differential aging.