Time Travel -theories and hypothesis

[Renegade]

Is time travel possible?
Is it feasible?
What is stopping us?
is it even difficult?

Time travel is a notion that on some levels is an accepted fact of our cosmos. As Chris pointed out on the most recent episode (what inspired me to start the thread) a subjects rate of movement through time is directly related to our rate of movement through space. This may seem odd but through Einstein we know that space and time are but two threads interwoven with gravity in the fabric of our universe. They are so related, in fact, that we may jump to the conclusion that instead of space and time being two separate axis of reality we may simply refer to this as Spacetime.

The simplest way to explain why we think it's possible to travel forward through time by going really really fast is actually quite simple. It is based on the law that nothing can ever go faster than the speed of light (until the numbers are back from Cern anyway). This is not because Light is just the fastest thing around, but we think that when you approach that velocity, your rate of acceleration appears to decrease when viewed from another vantage point. To put it simply, if two cars were going 99% lightspeed side by side and car A slams on the gas he would see himself going quite a bit faster than car B but car B would see Car A slowly inching past. Car B stops ten minutes later and Car A as well, when the discuss the ride they would find that while Car B drove for 30 minutes, Car A only drove for 5.
To support this we have simply to look above us. The GPS system of satellites are equipped with the most accurate clocks man has ever made, so accurate that if they were off by one microsecond, the GPS system would be thrown off by about 300 meters (really really good clocks). We've found that after long enough time orbiting earth at a rate of 2 orbits and day, the clocks in every satellite would be off by about two billionths of a second.


If a one-way ticket to the future isn't your thing, I'm afraid you're looking at a much wackier set of problems, paradox's and possibilities.

"Grandfather Paradox"
Thought Experiment:
Let's say you have a time portal; a gateway to 100 years ago. let's also assume that you go through it and chill out in 1912 no problem. Now you find your grandparent/greatgrandparent and kill one before giving birth to your parents/grandparents thus meaning you are never born. This creates a paradox, something that just can't work and if we think about it too much we might just go mad from the revelation and flee from the light into the peace and safety of a new dark age.



What if instead of going back in the timeline of our universe, we went back in time in a parallel universe (as theorized by quantum physicists)

Thought Experiment:
Let's say you have a time portal; a gateway to ten minutes ago. The first and possibly the largest detriment to your vacation in time is one of the oldest and most accepted laws of Newtonian physics; Matter and Energy cannot be created or destroyed.
By simply turning on the machine and pointing a flashlight through it, you are taking energy that rightfully belongs in this universe's timeline and adding it to your destination's universe! The only way for reality to keep making sense is is an equal amount of energy/matter to be feed back into the system which lost it. We have now made a feedback loop that will continue to increase until our machine explodes/implodes/turns into a gibbering pile of tentacles and horror.



discuss?

[old book]

On the quantum gestalt, perhaps quasars are white holes spitting back equal measure what the black holes are sucking into Universe B? Heheh. I know, I know, black holes are "singularities" and the mass isn't really going anywhere... for now. Whatever "now" is.

How bout we don't pass ourselves, matter or energy to other times, but consult a sort of record of all times in order to time-travel exclusively through information? Or how bout mental time-travel where we can gain information and maybe even exert some sort of limited influence. Whatever time is in our universe, it sure seems like a singularity whence we cannot escape. I'm sure there are still deep secrets and mysteries involved in gravity, time, magnetism and other forces and phenomena.

I sort of giggled when Sich asked Chard if time travel were possible, and Chard answered seriously. It's a good question, but I would just have to say, "I don't know, but I hope so, because time seems oppressive at times."

On the title of the story, the idea that something can cast a shadow through time, backward and forward, is very interesting. I think there is something to it. If it were possible to catch a bit of it, we could prophecy upcoming events, which is a sort of time travel. Fortunately or unfortunately, next week's little league game being cancelled because of heavy snow doesn't seem important enough for our time-antennae to catch a whiff of, but the game being buried under volcanic ashfall might be, which makes the whole matter really rather subjective, based on personal categories of importance instead of cosmic significance. Then again, there is no such thing as coincidence if there is no one there to understand that a coincidence has taken place.

[Renegade]

....How bout we don't pass ourselves, matter or energy to other times, but consult a sort of record of all times in order to time-travel exclusively through information? Or how bout mental time-travel where we can gain information....

To transfer and/or interpret information between anything requires energy (Binary/nerve stimulus) or matter (written information).
Information itself does not exist exclusive from any means of storage or interpretation whether computer, Human, animal or otherwise.
:-)

[old book]

Hmm, well, that's the point I was making about how coincidence/synchronicity cannot happen without an observer to observe it. There might be a kind of information--information also depends on an observer to distinguish it from noise--that doesn't depend on material, not even "spooky" pseudo-quasi-instantaneous "information" passing between entangled quanta at great removes from one another.

[Eric Lofgren]

I am familiar with what Chris was saying about time travel; that if a time machine was created you could only ever go back to the point at which it becomes fully active. I'm just not sure if it's because you have to have a machine at either end, though. I'd always assumed that it was a quantum thing where once time travel existed quantum rules had somehow changed and a new dimension is created. Riffing on the observer principle maybe? Or am I just saying the same thing differently?

At any rate, no discussion of time travel is complete without a reference to this gem- http://www.youtube.com/watch?v=Gj3qesTjOE8 This is just a snippet. There is quite a lengthy explanation found here-http://www.youtube.com/watch?v=Y6a4T2tJaSU. Whatever the case may be, that could very well be the good beetle Swami trying to pass himself off as an Earthling. Or even a Yithian based on the body shape    

[Genus Unknown]

I just have to nitpick Chris's description of how relativistic time travel works. Nothing "slows down." If you're on a spaceship traveling near light speed, you don't age any "slower." It's just that the quirky nature of time starts to become apparent when you look at events from two different reference frames of movement, and the faster you're moving (relative to something else), the more apparent it is.

The example that sticks in my brain most is from Simply Einstein: Relativity Demystified by Richard Wolfson. I'm sure it's been used elsewhere, but that's the book I read it in.

Say you have a rectangular box of x length. At one end is a flashlight (point a), and at the other end is a mirror (point b). You turn the flashlight on (which we'll call event a), and the beam of light travels down the length of the box, bounces off the mirror, and returns to its starting point (which we'll call event b). Now, since we know the speed of light, c, and we know the length of the box, we can calculate the distance the light travels, and from there calculate the time between those two events (which we'll call t).

Now, the value that you get for t will depend on your frame of reference, specifically whether or not you are moving relative to the box (or the box is moving relative to you). If you're at rest relative to the box (i.e., the box is "at rest," to use the intuitive but incorrect term), the length the light travels is twice the length of the box, or 2x.

BUT -- say the box is moving sideways relative to you, the observer. Suddenly that calculation doesn't work, because the light is no longer simply traveling 2x. Sideways motion has been introduced into the equation. It's not traveling to the same point and back; its path, if you charted it out in three dimensions, is diagonal. It starts at point a, hits point b in a different location (from this observational standpoint), and returns back to point a, which is also in a different position (from this observational standpoint).

In other words, depending on your state of motion relative to the box, the light takes a shorter or longer path. And since the speed of light is constant regardless of your state of motion (for reasons I can't go into here), it necessarily follows that it took a different amount of time to travel between those points. So t, the time elapsed between event a and event b, is actually variable. It depends on whether or not you, the observer, are moving relative to the box.

TL;DR -- the time elapsed between any two events is variable depending on the observer's state of motion. The Universe is fucking weird.

[old book]

A good way to get a grasp of Genus's box and mirror example is to turn the light on in the bathroom, then turn the taps on just enough to get a constant drip. Watch the rate of the drip. Now, assuming everything is in the right place, watch the shadow cast by the drip upon the tub. It's the same rate, but the distance travelled and speed appear differently.

Also: Quetzalcoatl comes as a laser show at a rock concert in the night, stealing upon one unawares. He is neither a snake nor feathered, but you can see how people might come up with that.

[Genus Unknown]

A good way to get a grasp of Genus's box and mirror example is to turn the light on in the bathroom, then turn the taps on just enough to get a constant drip. Watch the rate of the drip. Now, assuming everything is in the right place, watch the shadow cast by the drip upon the tub. It's the same rate, but the distance travelled and speed appear differently.

I'm... not sure what that has to do with the mirror-box example. What you're describing sounds like an optical illusion, whereas the mirror-box example is about the actual time elapsed being different depending on the relative motion of your frame of reference.

[old book]

I guess just that the speed of light remains the same despite seeming discrepancies and different appearances. The shadows of the drops move faster or slower depending on the angle of the illumination, but the rate of dripping--the speed of light--remains the same. To compensate for a shorter apparent distance travelled by the shadow drops, the apparent speed is decreased. A longer apparent path of the shadow drops results in a faster apparent velocity. Accelaration actually, since the drops are accelarting under gravity. Likewise, when near-light velocity or accelaration comes into play, time slows down as if to compensate for the length of the path traversed by light. Maybe it's simpler than the mirror and box example, or maybe more complex, or maybe just a bad example. Or maybe it only works in my shower, and you had to be there

[Genus Unknown]

Or maybe it only works in my shower, and you had to be there

Who says I'm not?

[Chris Lackey]

I knew I had that coming. As we record I remember these half-truths and then interpret them as best I can. If only I had a time machine I would go back kill Newton. Or just fix podcast mistakes. That's it.

[Genus Unknown]

Don't kill Newton! That'll make gravity stop working!

[old book]

Or maybe it only works in my shower, and you had to be there

Who says I'm not?

Excellent point.

[Jake W]

Understanding of time travel needs a better grasp of what time/space actually is. "Information" can mean something other than recorded data and there are theories around that the smallest level you can break reality down to is 'information' of a sort.

Everything that happens is the most probable occurance out of all possibilities, but how can the universe know what is most probable? How, for that matter, can light know which is the most direct route to travel?

The answer lies in the way waves move. Waves are the effect of energy on a medium, the medium itself moves a relatively small amount as energy passes through it. Light waves travel in all possible directions at once, but those which don't go the most direct route intefere with themselves (Stop smirking Fifer!) and are cancelled out. The one that remains is the most direct route from A to B.

The universe can be described as a wave, and I suspect the medium it travels through is 'possibility'. The wave form is what's most probable within all that's possible. But to get this it has to travel instantaneously through all possibilities. Everything that can happen does, but is instantaneously cancelled out and only that which is most probable remains along the wave with no interference. This narrow band is what we naively call 'reality'.

To travel back in time you would somehow have to get the whole universe to rewind through all possibilities and stop at the point that took your fancy. Wormholes might allow a window on the past, but anything travelling there would change the path the wave took and make a new wave. The paradox is this would mean causing a new universe to appear (i.e. spontaneously creating a whole universe worth of new enrergy, and that's not possible) and/or wiping out the time traveller's departure point (essentially the same problem as the 'Grandfather Paradox').

HPL's psyche-based time travel is a neat solution as it offers a balance. The time traveller swaps places with someone else whose actions can be a known quantity so there's no paradox. Physically nothing changes and only the probability of the 'present' (the futuremost point) alters, but with no energy debt and nothing to replace in the past. All the gaps are filled. Actions taken by the time traveller won't necessarily affect anything in a way that's hard to explain and HPL doesn't have (as far as I know) time travellers going over each others' paths changing timelines.

How the connection through time is made I couldn't say, but the principle isn't something we can dismiss when you consider the mystery of Pauli's Exclusion Principle ( http://en.wikipedia.org/wiki/Pauli_exclusion_principle ). If all atoms can be connected in this way then there are probably other connections we don't even know about yet.

[old book]

Excellent points, Jake W. As good as Genus in my shower, at least

The symmetry or balance of swapping bodies is good, but there is a problem Lovecraft failed to address really: if a person from the present Earth is sucked back a million or so years to be a rugose tentacled cone slug for a season in a city surrounded by strange gardens with extinct plants, and the rugose cone slug takes over his body in 1919 or thereabouts, the future being going back into the past could give rise to "information" which violates cause and effect. Now hold on, I know what you're saying, and yes, your point was the conservation of energy so new universes don't have to appear ab nullio, with no apparent source for all that energy and mass, but I'm not defending cause and effect, I'm only saying Lovecraft is stuck in that paradigm even as he violates it, because he speaks of certain instances where the Elder Great Ones or whatever they're called faced imminent danger CAUSED by leaks of memory in the far-flung future. In fact every retrograde motion of a being back in time would present such leaks of impossible information that these new universes would have to branch continuously into being.

What I really loved about SOOT, which I'm referencing poorly above, is the part about how the Big Slugs bribe the carnal prisoners with library and travel privileges. NO, DON'T RESCIND MY LIBRARY PRIVELEGES!!!! THE COSMIC HORROR OF IT ALL!!!!