time and motion - is the mathematics understood?

[astroboyuk]

A general question for anyone out there who might know:

the thing glossed over by just about every time travel story is that simply moving through time wouldnt be very helpful. If I went 24 hours back in time, but no where 'geogrphcially'... I would find myslef floating in space... because exactly 24 hours ago in that spot, the earth was still a day away from where I am.

If I travelled back in time 1hour, I might be lucky enough to still be on earth somewhere, but perhaps in the the middle of the sea... etc.

So to time travel in the traditional sense, there is also an implied assumption that we are alos travelling in space/dimension simulteanously, so that when we appear in the new time, we are more or less in the same spot as when we departed.

So!, my question is: would the mathematics for knowing how far you have to move in space to match your movement in time be straightforward to work out, or would you have to basically have a formula for the movement of the entire universe, or at least our solarsysem in relation to the universe?

Would it have to be very complex or could it be somewhat simpler than I think? Im curious.

 

[Mylo.X.]

A general question for anyone out there who might know:

the thing glossed over by just about every time travel story is that simply moving through time wouldnt be very helpful. If I went 24 hours back in time, but no where 'geogrphcially'... I would find myslef floating in space... because exactly 24 hours ago in that spot, the earth was still a day away from where I am.

If I travelled back in time 1hour, I might be lucky enough to still be on earth somewhere, but perhaps in the the middle of the sea... etc.

So to time travel in the traditional sense, there is also an implied assumption that we are alos travelling in space/dimension simulteanously, so that when we appear in the new time, we are more or less in the same spot as when we departed.

So!, my question is: would the mathematics for knowing how far you have to move in space to match your movement in time be straightforward to work out, or would you have to basically have a formula for the movement of the entire universe, or at least our solarsysem in relation to the universe?

Would it have to be very complex or could it be somewhat simpler than I think? Im curious.

Good question. I have no answer, but would just add that time-travel is a misnomer. It should be referred to as Space-time-travel, for the very reasons you have pointed out.

 

[Einstein]

Generally it is believed that time and space are intimately intertwined with each other. So moving through time should be connected with moving through space too. Six months ago the earth would be on the other side of the sun. So if your time machine were to take you back six months in time, you wouldn't wind up in space as is sometimes believed. Six months ago the space you are in now was six months younger and existed on the other side of the sun with the earth.

Also another thing I have noticed is that no one ever takes notice of gravity and its relation to a time traveler. A time machine would allow motion through time-space along the time axis. Gravity seems to have a zeroing effect on the local time-space. The local space appears as if it is being dragged by the earth in its journey around the sun. In effect our instruments show very oddly that the earth seems to be standing still, while the universe is moving about us. I cite the Michelson Morley experiment as the measuring tool that demonstrates this odd phenomena.

 

[astroboyuk]

in a universe in which all bodies are in constant motion, the idea that anything rotates around another thing is arguably subjective!...

but in regards to your post: I find that concept (space and time to be so closely intertwined that you'll just move to wherever you were in relative terms) difficult. Isnt the idea of time travel that it is actually breaking the nexus of time and space ? or to ask another way... why should time and space be so connected? are you saying that is (in the simpliest terms possible) - the agency of gravity?

 

[Darby]

A general question for anyone out there who might know:

the thing glossed over by just about every time travel story is that simply moving through time wouldnt be very helpful. If I went 24 hours back in time, but no where 'geogrphcially'... I would find myslef floating in space... because exactly 24 hours ago in that spot, the earth was still a day away from where I am.

A good question.

Remember from Einstein and Minkowski that time and space in both Special and General Relativity are treated as one 4D "space" called spacetime. To navigate in time you would need a 4 dimensional coordinate for your target: x, y, z & t.

Just how we do that, navigate through space and time where time is a variable with three signs (plus, minus and imaginary), is a bit of a problem. In fact all four axes of the system of spacetime coordinates are complex - they all include i (imaginary) as one possible sign.

Anyway, if you had the knowledge, technology, engineering and ability to build an actual time machine you would have to also develop the navigation system starting with the theoretical physics and ending with the applied engineering.

 

[astroboyuk]

A good question.

Remember from Einstein and Minkowski that time and space in both Special and General Relativity are treated as one 4D "space" called spacetime. To navigate in time you would need a 4 dimensional coordinate for your target: x, y, z & t.

Just how we do that, navigate through space and time where time is a variable with three signs (plus, minus and imaginary), is a bit of a problem. In fact all four axes of the system of spacetime coordinates are complex - they all include i (imaginary) as one possible sign.

Anyway, if you had the knowledge, technology, engineering and ability to build an actual time machine you would have to also develop the navigation system starting with the theoretical physics and ending with the applied engineering.

agreed: and would the development of the navigation system itself be realtively (no pun intended) easier than mastering time travel itself?

 

[Darby]

agreed: and would the development of the navigation system itself be realtively (no pun intended) easier than mastering time travel itself?

They would have to go hand-in-hand. Understanding the meaning of "navigating spacetime" in the sense of a time machine necessarily includes understanding spacetime itself and how to circumvent our limitations on moving through that space. Once you have that understanding the engineering starts falling into place. But would it be easy? I don't imagine that it would be an endeavour where the word easy would ever enter the lexicon. Spacetime is the very fabric of physical reality. It is the stage upon which reality is played out. Time travel is the manipulation of the fabric of reality in ways that are not known to naturally occur, with the possible exception of areas at and interior to the event horizons of black holes. But even there we are stretching the meaning of "natural events" to the extreme edge of physics.

 

[astroboyuk]

They would have to go hand-in-hand. Understanding the meaning of "navigating spacetime" in the sense of a time machine necessarily includes understanding spacetime itself and how to circumvent our limitations on moving through that space. Once you have that understanding the engineering starts falling into place. But would it be easy? I don't imagine that it would be an endeavour where the word easy would ever enter the lexicon. Spacetime is the very fabric of physical reality. It is the stage upon which reality is played out. Time travel is the manipulation of the fabric of reality in ways that are not known to naturally occur, with the possible exception of areas at and interior to the event horizons of black holes. But even there we are stretching the meaning of "natural events" to the extreme edge of physics.

Mmm.. so would the time machine also need to have a propulsion system or some other means of movement? of the movement would be wrapped up in the distortion of time space- so the two are indistinguishable.

Also from what youre saying, the ability to move through time would involve maths required for 'geographical' as well as 'temporal' movement... but having said that, you would not have to actually employ both in the process, would you?: ie you could argauably choose to move in time but not move geographically (for whatever crazy reason). I wonder if the engineers of the future end up saying: I can get you through time, but the pin-point geographical requirement doubles the power we need or needs a new widgit to make it work.

 

[Darby]

Mmm.. so would the time machine also need to have a propulsion system or some other means of movement? of the movement would be wrapped up in the distortion of time space- so the two are indistinguishable.

Also from what youre saying, the ability to move through time would involve maths required for 'geographical' as well as 'temporal' movement... but having said that, you would not have to actually employ both in the process, would you?: ie you could argauably choose to move in time but not move geographically (for whatever crazy reason). I wonder if the engineers of the future end up saying: I can get you through time, but the pin-point geographical requirement doubles the power we need or needs a new widgit to make it work.

The word you were probably looking for is geometry. And, yes, General Relativity absolutely involves geometry. Einstein, while working out the solution to GR had to go back to school and study post graduate level analytic (hyperbolic) geometry - the study of non-Euclidean coordinate geometry of curved space in terms of algebra/calculus.

Propulsion System

As stated, we move through spacetime. We don't seem to need an outside source of "propulsion" to move along our time vector but we do need to expend energy to move along our space vector. So we probably do need some sort of propulsion to move in space with our time machine.

On the other hand a time machine itself implies displacement in space. It's a "simple" rotation of the axes. Move along the time axis, rotate through some angle and we're moving along a space axis as well as the time axis. Scare quotes on simple because stating the fact is easy, actually doing it if far from simple.

As an aside, this is something that was pointed out to Titor relative to his "stationary mass" handwaving description of his gadget. He didn't get it. Just more handwaving. Dr. Robert Brown (Duke University, Physics Dept) pointed out the same falacy when he posted his thoughts on Titor's story.

 

[astroboyuk]

oh god, dont mention the Titor! I cant stand that bs... but I get all the other bits youve explained, thanks.

Are you from a physics background?

 

[Mylo.X.]

. Spacetime is the very fabric of physical reality. It is the stage upon which reality is played out. Time travel is the manipulation of the fabric of reality in ways that are not known to naturally occur, with the possible exception of areas at and interior to the event horizons of black holes. .

Would you consider the sporadic occurences of "time-slips" a natural manipulation of reality? Or do you reserve judgement as to whether or not these (time-slips) are real experiences?

 

[Darby]

oh god, dont mention the Titor! I cant stand that bs... but I get all the other bits youve explained, thanks.

Are you from a physics background?

No, not a physics background. I took enough undergraduate physics courses to have a reasonably good understanding of the basics. My major was experimental psychology.

 

[Darby]

Would you consider the sporadic occurences of "time-slips" a natural manipulation of reality? Or do you reserve judgement as to whether or not these (time-slips) are real experiences?

I'm sorry Mylo but absent physical evidence, repeatable experiment and independent verification of "time-slips" I wouldn't consider them to be manipulations of reality or even reality itself. As far as I know it is a Kurt Vonnegut creation to explain Billy Pilgrim's otherwise PTSD related psychotic delusions in Slaughterhouse 5 (Billy is "unstuck in time").

 

[John Thomas]

What if geographical location wasn't an issue at all?
If I rewind a video and I go to the beginning of the movie, the video pre-determines the geographical location.
The past might be perfectly anchored to the present.
My smart phone contains my oily fingerprints. In some places, the phone might still contain the oil from my fingers that I put on it the first day I used it.
Those fingerprints might be geographical markers.

 

[astroboyuk]

What if geographical location wasn't an issue at all?
If I rewind a video and I go to the beginning of the movie, the video pre-determines the geographical location.
The past might be perfectly anchored to the present.
My smart phone contains my oily fingerprints. In some places, the phone might still contain the oil from my fingers that I put on it the first day I used it.
Those fingerprints might be geographical markers.

So how might that work mathematically? If we're talking about hte mathematics of pinning down time and place.. how would you use that information programatically?

 

[Darby]

What if geographical location wasn't an issue at all?

Then we would have a serious problem. "Geography" (geometry) is General Relativity. If spatial coordinates are irrelevent then General Relativity is falsified. But all time travel theories come from General Relativity. By falsifying GR we simultaneously falsify all time travel theories.

 

[astroboyuk]

Darby, given that we have (for purposes of this discussion) agreed that geometry and temporal travel are irreperably intertwined.. how would you imagine this would be managed by the engineers running the system. If the mathematics were known would it be a case of dialling in the 'co-ordinates' just as we see on many a time-travel show, with a nice, apple-esque user interface to make it easy? How many parameters would you need to pump in to achieve a given time?
and could you actually set it to travel geographically a long way, but only 1 second in time... so that a time machine could actually be transport/teleport machine as much as anything else?

 

[Darby]

If the mathematics were known would it be a case of dialling in the 'co-ordinates' just as we see on many a time-travel show

Dialing in the coordinates relative to what? We specify Earth coordinatess when traveling from A to B relative to the surface of the planet based on radial coordinates from one or both rotational poles (longitude) and the rotational equator (latitude). Specifying coordinates for a non-local target is something of a challenge. You can't see, touch, smell, hear or taste the past or the future as you can with, say, Detriot or London. They are physical things that can be sensed and localized with great accuracy. How do you specify coordinates for something that is not only non-local but is no longer even a part of your universe? Toss in Many Worlds Interpretation where your interaction with events creates infinite universes, also non-local and not a part of this universe by definition then you have possibly insurrmountable problems. Target acquisition requires a feedback system to let you know that the target is acquired. There's no feedback system here.

But that's the difference between theoretical physics and mathematical physics and; applied physics and applied engineering. Having a theory is wonderful. Making something practical from theory is entirely different and involves a seperate set of challenges.

 

[astroboyuk]

good post, spot on...and I guess thats what Im on about when I say 'practicalities'.. is the engineering aspect.

If goinga long way backwards in time, you'd have to send out a few probes to the destination point and hope to be able to retrieve the information manually (a message in a bottle system),.. going forward in time a long way would be very dicey - as there's not feedback look (unless someone from the future travelled back to you first and told you!)

If going back or forward a short way you could probably have a bit more confidence in the destination charachteristics.

In terms of the mode of transporting a normal human being.. I struggle to imagine it not being a vehicle of some kind that moves everything safely within it... I dont see how a backpack version can have enough to enclose a whole person/s.. and know what parts of the immediate area to take and what to leave behind...

 

[Darby]

I struggle to imagine it not being a vehicle of some kind that moves everything safely within it...

Thank you for the comments and kind words.

I agree on the necessity for a vehicle. Ultimately it depends on the actual solutions to GR as to what a time machine entails in the practical sense. For now we have Kerr-Newman black holes (KNBH) - both charged and spinning. In a Schwarzschild BH the Penrose Diagrams terminate in the "shark's teeth" - certain death for the TT at the singularity which cannot be avoided once s/he crosses the event horizon. The KNBH theory states that the angular momentum creates a ring singularity that can, in theory, be traversed into another universe, somewhere else in this universe and into the past or future. The KNBH Penrose Diagram allows one to avoid the shark's teeth.

Aside from needing "exotic matter" to keep the throat open on the wormhole associated with the ring singularity and discounting the gravitational tidal forces inside the wormhole, you have to deal with the fact that the KNBH is electrically charged. Not just a slight charge but maximally charged. The inside of the wormhole would be far, far worse than a normal lighting bolt. A TT would have to have a vehicle that could, somehow, withstand trillions of volts and trillions of amperes. The vehicle would truly be an engineering miracle to create. The electric potential is >>> greater than the electron binding energy on the atoms that would make up the vehicle. Absent virtual magic the atoms of the vehicle (and our brave adventurer) would be stripped away leaving an ionized nuclei soup.

Of course we have yet another huge problem. There are no black holes in our neighborhood let alone a KNBH. If we did find one and we could somehow go to it, it would be a very long trip. The nearest star outside the Solar System is 4 LY away and there is no black hole there. And we'd have to find the right KNBH, one with a wormhole whose throat would be several hundred kilometers in diameter (tidal forces necessitate a huge throat). That would mean a KNBH with a mass of hundreds, if not thousands, of Solar masses. Stars super nova to make a BH. In so doing they lose a great portion of their initial mass. So the "star" that created a several hundred Solar mass BH was far greater than the mass of the BH itself. Stars, unfortunately, don't come with that sort of mass. Near the center of a galaxy is where you would find such a BH because stars are much closer together and collide, eventually reach a critical mass and super nova. Going to the area near the center of a galaxy would not be much fun.

Note: "Trillion" is the American useage, 10^12, not 10^18 as in the UK.