Time Travel!

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Somehow, saying it twice does not make it more convincing.

Right you are. I apologized. It was not intentional.

Why would you want to?

If I stand still for precisely one second then I would have travelled one second into the future. OMG EINSTEIN REFUTED!! !

What I want to know is, what the hell is this doing in the art, writing and music board?

Life can sometimes be very mysterious.

PLANCK'S VERSE

From under Euclid's hat
Where space is very flat
The points dance out to anchor skeins of lines
Forming abstract mediums
Subservient to axioms,
Hypotheses and theorems that underlie designs
Which articulate extensions
Of the classical dimensions
Where the ideal and the concrete intertwines.

But something misty-hazy,
A modicum quite crazy,
Infected lines selected parallel.
It was hard to put your finger
On the doubts that tend to linger,
But they rang an alien brass bell.
When scrutinized with rigor

They simply wouldn't figure -
A discord most difficult to quell.

With the grace of an Eglevski
Along came Lobachevski.
He'd an eye to Euclid's parallel device.
By combing suppositions
He discovered new conditions
To make the general precise.
With Riemann he played games
With mathematic aims
And invigorated space with new spice.

Einstein looked at Newton's space.
He measured to the millionth place
And discovered something really wasn't right.
At orders of high magnitude
He found old concepts came unglued,
Especially at speeds close to light.
"The problem is," he had to state,
"Space is really not quite straight
But somehow strangely slickly subtly skewed."

How it's curved, he could not say.
It could be almost any way
Dependent on the mass proximity.
It needed no great miracle
For fourth dimension spherical
But then, in equanimity,
Theories deployed
Hyperbolic paraboloid
Held truth in anonymity.


"This space", he said, "I must
Most radically adjust
By fusing it confusingly with time.
So that the present, past and future
Are joined in special spacial suture.
Not in plan Satanic nor sublime."
Since time is also space
In each and every case,
We should call it tace or, maybe spime.

But events within this framework
Became, no longer, tame work.
The kingdom of the random becomes rife.
Uncertainty is certainty,
Will becomes insanely free,
And God is playing craps with your life.
So, if you are late for dinner,
You no more are a sinner.

Modern physics will explain it to your wife.

That's...well, average.

For a start, it's far too long and rambling. I know of only a handful of great poems that are nine stanzas long, and The Raven is one of the few I like, because it tells a story. Yours doesn't, it's just topical, and that makes it uneccissarily bloated.

Technically it seems a bit sloppy for a poem. You start in Iambic Pentameter, then you drop it here and there, and it's quite jarring.
You don't use much in the way of imagery, more metaphors and a few similes would make it more evocative.
Also, some your lines are too long/have too many syllables for ABBA/ABAB poems, when spoken aloud the rhyme is lost amidst the jumble of jargon.

You're clearly good at rhyme, but your flaws are a bit obvious.

Post another, I want to see that forty years of experience. I might post some of mine in turn.

I dunno; I think that the twin paradox doesn't travel into the future, so much as they both experience the same time, just at different rates...

If I have this right (I'm only Sunday Supplement in science..., then it would take infinite energy to travel at the speed of light. So all temporal movement is forward (tachyons notwithstanding)
moving backwards, is not proven...am I right?

But then, I've never been able to tell the difference between General relativity and special relativity, other than the Special one rode on the short bus... j/k...

The twin paradox doesn't rhyme very well either, but it does have a humor potential.

Well, the reason time travel is of any interest at all is that it isn't complete BS, actually. I believe the infamous logician Kurt Goedel was the first to find a solution in general relativity which allowed for time travel (in Goedel's universe, as I recall, one could travel into earth's past simply in a space ship- weird stuff, but then Goedel was a weird guy), but the point is that several solutions to GR exist in which time travel is permitted. While, on the one hand, there is certainly no corroborating evidence for this, to my knowledge, on the other hand it does have a modicum of theoretical support.

What was infamous about Goedel (other than his work with the vienna circle, and a little bit of craziness near the end of his life)?

[Note: Now I am sort of speaking to a generic audience, twoshots.]

Yeah, General Relativity (GR), has some solutions which seem to allow for time travel. Special Relativity (SR), does not, nor does it talk of it at all. It just defines time in a way that allows physics to work the same, no matter how fast you go. (basically, if the speed of light was not the "speed limit", physics would go haywire. You could basically see "frozen light", and you can send yourself a light pulse signal, before you sent it.).

Trivia note: One thing to note is that we physicists don't talk about "time travel" but rather "Closed Time-like Curves" (or CTC). It is a running gag amongst physicists because we all know we are talking about time-travel, but we put CTC on our grants in order to get funding. Plus it makes us sound less crazy. So if this thread said, "New calculations for Closed Time-like Curves", I would first think I was on Arxiv.org, or some other physics site, then I would think there was some real physics going on in the thread, heh.

But GR, as it works, suggests some possibilities. Some have been discounted, but most are merely "impractical" (but not unphysical). The special types of black holes that allow for worm holes (not all do. Typically it has to be rotating.), seem to be physically possible. But once matter or energy passes through them, they would immediately collapse.

Then as twoshots said, there is something called the "Goedel universe" which allows for time travel. That is a special case solution to Einsteins equations in GR.



Einstein's GR equations/equation (aka the Einstein field equations):
Basically, Einstein's main general physical result in GR is summed up in this equation,

.

(sorry if math scares some of you...>.<)

Basically, the left hand side of that equation is just "math" (specifically geometry. Yuck. I hate geometry!), while the right hand side is "physics". Some of you understand what I mean by that already, but for those of you that don't, understand that physics is not math, but it does use math. For math to be relevant to physics, it must reference and be used to describe physically observable phenomenon.

So basically it reads like this:

[Geometry of 3+1 dimensions with warped space] = [Matter and energy density].

As you can see, mathematicians can talk about geometry with curvature and warped space all they want until they are blue in the face. They can talk about surfaces, topologies, shapes, polygons, in all numbers of dimensions, but it does not mean a thing to reality without some physical "stuff" to talk about. That's the left hand side. It is just complicated geometry. The right hand side describes the density of matter and energy in some region of real space-time (like your backyard, the entire planet, a black hole, the entire universe, or perhaps another universe).

Thus this equation describes how the density of matter and energy warp the geometry of space-time. That letter big "G" in there is a constant called the "gravitational constant", and thus connects the curvature of space-time to what we call "gravity".

That little "g" with the subscripts is called a "metric". Basically it describes how you measure distance in what ever funky curved space geometry you are talking about. Basically, it is the answer to the question, "what is the shortest distance between two points?". If you looked on a piece of paper, and made two dots on the paper, the answer is a straight line. But if you made a tube out of the paper, the shortest distance is to poke a hole through the paper at one point to reach the other point. That still looks like a straight line, but not if you were on the surface of the paper. If you can imagine it, imagine the straight line cutting through the sides of this paper tube. As you unroll the paper back to its flat state, that straight line would go in a curve beneath the flat paper and then reach the other point.

Take another example. Whats the shortest distance between New York city and Rome, Italy? (through the TARDIS of course!). Well it would be through the earth, but you can't do that. But if you could that would be a straight line. Thus, since you have to travel over the surface of the earth, the path you must take is a special curve. This curve is called a "great circle" or "geodesic" and it is the curve that is part of the largest circle you can make on a sphere.
Here's a nice animated gif demonstrating this,

.

If you want further details, you can check it out on the hosting site here, http://www.black-holes.org/relativity5.html .

So when I talk about metrics, that's what I mean. The thing to keep in mind though is that we are not just talking about two points in space, but in space and time.

The einstein equation is complicated because of those subscripts, and the fact that the geometry is complicated, and there are first and second order derivatives hidden in that.

Those subscripts can be viewed in two ways. One way is to imagine the variables with the subscripts, R (the first one), g, and T, as 4x4 matrices with 16 variables of their own, each. Or you can view this one equation as really 16 different and unique equations that you have to solve for all at the same time to come up with a complete solution.

Thus, how should I put this. I think the typical NT expression would be, "This mother fuck-ing s**t is hard!! !". A complete solution is not known. Only solutions for certain special cases are known, and some of those contain physical numbers that we don't know yet.

In the interest of full disclosure, I cannot solve any special case, even the simple flat space case, but I might be able to if I worked at it for a while. But I have yet to try it. I likely would never bother trying to find a new solution to the Einstein GR equation because that is really just about creating new fancy and complicated math, and I don't like math. For physicists, the right hand side is easy, but even for mathematicians, the left hand side is hard, hah.

So yeah, why did I describe all of that. Actually, I forgot a few times while writing this. At some point I convinced myself that it had something to do with describing Godel's universe and the Tipler cylinder, and maybe wormholes. So I will believe that if you will.

So yeah, I know of 3 solutions to the Einstein equations (err, I might saw "equatioNS" or "equatioN" without realizing it, sorry. But you know now there are infact 16 equations there.), that allow for time travel. I "know of" them, but I don't understand them and cannot rederive them.

The most famous is the wormhole. Then the other two aren't well known at all. They are the Godel universe, which does not apply to our universe at all. hah. Then there is the Tipler cylinder, which was thought to be physically practical, but turns out that it could never be built.

Wormhole:
On the right hand side of the equation you stick in a the description of the mass and energy of a rotating wormhole. Then you try to figure out everything else. One of the most interesting things to figure out is the metric little "g". For such a black hole, the metric is very complicated, but it describes one possible path that leads to a "white hole" "somewhere else" in space and time. It does not have to be time travel, but it can merely be anywhere, anywhen.

But there are two major problems. First is that the mouth of the wormhole is unstable. Einstein's equations work there too. As you know, you put mass in some region of space, and then look to see how it curves. So once you introduce enough mass in the mouth of wormhole, this changes the curvature such that it collapses.

This might be able to be prevented using "negative energy" which is like "negative pressure". You put this stuff into an inflated helium balloon, and the balloon will deflate, but still float. Current physics can't really produce enough negative energy to do that. Quantum Gravity (QG) might be able to, but that is a future theory we don't have yet.

The second major problem is, where are the white holes? Not only have they never been observed, we know of no astronomical phenomenon of making one. Astronomers have really looked hard for these things. And NO, they are not quasars or anything other stellar body that we know about. But I call this the second problem because, it might just mean that you end up in another universe or something. Like one where your the NT, and everyone else is an aspie!

Trivia note: The term "Wormhole" was coined by Carl Sagan and Kip Thorn for Sagan's book "Contact", which was made into a movie a few years ago starring Jodie Foster, I believe. In fact, Sagan called up his physicist friend Thorn to come up with a new feasible way to travel faster than light. So Thorn came up with the physics behind wormholes for a science fiction book for his friend! hah.

The Godel Universe: Like I said earlier, Einstein's GR equation can describe the entire universe, or even an entire universe, heh. Now imagine a universe filled with a loose cloud of particles, like a cloud of dust. The entire universe is "rotating" (however, I don't understand the math enough to describe to you what that means.). The universe is expanding, but the density of the mass is just EXACTLY right such that it keeps the universe from expanding and does not collapse it. It is perfectly flat.

Regardless of where you are in that universe, everything will appear to be rotating about you! If you look in certain directions, you will see yourself at an earlier time, though it would appear very far away. If you travel along this direction, then you will arrive before you left. This is because the entire universe is rotating, in addition to your own motion, so the past catches up to meet you. If you travel along a similar but different path, then you can travel to the future. In a sense you are moving along the rotation of the universe.

Our universe is not a Godel universe since our universe is expanding at an accelerated rate, and we can obviously see that we don't perceive the effects of a Godel universe.


Tipler Cylinder: Okay, lets stick to this universe. No possibility of traveling to another universe with this one.
A Tipler cylinder is just a massive rotating cylinder. It must be massive enough to have a gravitational pull on it, and it must be rotating fast enough to allow for sufficient "frame dragging", a phenomenon I will speak of shortly. The less massive it is, the faster it would have to rotate to produce the same effect, and vice versa. The balance can be met in achievable stellar terms.

So you know that mass and gravity warps space, but it warps time as well. However, the effect is more or less the same as time dialation. The more gravity you have, the slower your clocks go. But there is another affect that is not seen in SR, and this is frame dragging. For a rotating gravitational body, space-time will have a permanent and "fixed" twist in the direction of rotation. How big a twist depends upon the mass and the rotation speed. We currently have a satellite in orbit right now that is sensitive enough to measure the frame dragging of space-time around the earth, but the effect is very small. It will need to be up there at least a year or two before we get numbers that we can see, and they will be very small numbers.

Now back to our cylinder. Under the right practical balance of mass and spin, space-time will be twisted in the direction of rotation around the cylinder, and if you can twist it enough, then there will be paths against the direction of rotation about the cylinder that connect to the path, and paths along the rotation of the cylinder that connect to the future (that allow you to travel faster than light, with respect to the rest of the universe, but light also travels "faster", so, yeah, whatever, hah.).

So wow, this sounds super neat. Perhaps this could be built by some advanced civilization or in our distant future.... So... what's wrong with this idea?....
Amusingly enough, we are still debating that. First off, Tipler only proved this for a cylinder of infinite length because the math was easier. This has not been shown true for a cylinder of finite length, though Tipler beleived it should be possible (likely far from the top and bottom of the cylinder). But Hawking came up with a general theory called the "Chronology Protection Conjecture" that more or less says that "any viable time machine will blow up the moment it is turned on". Of course, it is more sophisticated than that, and the reason for the explosion is very simple and sound. However, whereas Tipler's calculation are pure GR, Hawking's calculation are not.

Physicists postulate that a theory called "Quantum Gravity" is needed to explain some stuff we can't figure out. Of course such speculation of such a need is perfectly okay, so long as we use that speculation carefully, when we still don't know how to explain that unknown stuff. Hawking's theory dips into the territory of Quantum Gravity a little bit. This is not at all bad, and perfectly reasonable, to a degree. It is done all the time in other fields between two different theories so much that it has a name, the "semi-classical approximation". Sometimes you can figure out just how far you can approximate things without knowing both of the theories you are "in between". But we can't do that for semi-classical gravity. We don't know how far we can dip into the QG territory. Hawking is likely at least partially correct, or maybe completely correct, but we will not know until we can directly test his theory, or we have a theory of QG.

So the Tipler cylinder might actually work?!?!..... maybe.... Or it might just be a huge bomb, haha. Anyone want to be the first Chrononaut for the Tipler cylinder? You just stand over here, while I stand over there, 20 light-years away behind that 2 light-year thick lead shielding, so that I can turn the machine on.

Huzzah! The end.




Wow, that was long. I did not quite intend to spend that much time writing something that no one will care to read, hah. I should do some physics HW and my research before I fail! And I should probably shower, but I am too hypersensitive to water. Ack! grr....

Here is a song for time travelers called, TIMETASTER.

http://iacmusic.com/songs.aspx?SongID=2 ... istID=8855

Done

indeed
this thread is a debate, not a short story or poem

I heard that time travel would create alternate universes. So it could actually be possible to travel into the past, kill yourself, and return to the future completely normal.

How do you move threads again? It was originally intended to be linked to my story "Return to Gallifrey" in the "Resurrecting Time Lords" thread. "Time Travel!" probably belongs in the Science, technology et al. forum, where it will be even more successfully disected by budding physicists.