You can go faster than the speed light and time travel? Sort of?

First, before anyone jumps on me for this, I understand most of the problems of having something with a positive rest mass exceed light speed and why it is essentially impossible.

What has me confused is an article I read in the August issue of Wired magazine titled A User’s Guide to Time Travel.

I will grant that Wired hardly counts as a scientific journal and their treatemt of what I am about to talk about is so amazingly thin for such a heady subject as to barely count as more than titillation. Nevertheless the article was written by Michio Kaku who has enough credentials to at least suppose he isn’t pulling things completely out of his ass.

All of that aside here is the meat of it (which you can read in the linked article):

Kaku mentioned a thing called a Van Stokum Cylinder that could be used for time travel (nevermind for the moment that making one seems impossible). In order to time travel you orbit this cylinder and depending on your direction you either move forward or back in time.

What I don’t get is the bit in the article where he mentions that to a distant observer it would seem as if the person orbiting the cylinder was exceeding light speed. How does the distant observer’s perception of what is happening affect me at all? In reality (as much as any of this could be considered reality) I am still not exceeding light speed whatever the other guy thinks so how does this get me to time travel? Except for time dilation caused by my movement I don’t see time travel here (and I don’t think time dialtion is time travel).

Clearly I’m missing something. Anyone else want to give it a shot?

[sub]I Googled “Van Stokum Cylinder” and got almost nothing. I tried “Van Stockum Cylinder” and, at Google’s suggestion, “Van Stokkum Cylinder” and still missed anything but one cite that required a subscription.[/sub]

It’s a van Stockum cylinder, named after the person who discoverd it (using GR), the problem is though that it’s assumed to be infintely long and therfore unrealistic.

Remeber that there is no absolute reference frame, so to the guy standing far away you are exceeding the speed of light.

I don’t have the patience to wade through all the Niven hits for “Rotating Cylinders and the Possibility of Global Causality Violation” to get to references to Tipler’s paper, so I will leave that as an exercise for the potential chrononaut.

I stipulated that this creature is essentially impossible (maybe outright, truly, 100% impossible…but never say never right?).

I figured reference frames were at issue but I still don’t see it. The distant observer sees me moving faster than the speed of light. Assuming he knows I am a chrononaut he should realize that what he thinks he is seeing is impossible (nevermind the impossible van Stockum cylinder I’m orbiting…pretend it is there somehow). He knows I have mass and that faster than light travel is impossible so he must be witnessing some sort of illusion.

Again, though, regardless of what the distant observer thinks he sees the fact remains that I am not moving faster than light speed. My reality may have me going very fast but not time travelling (as I would have to exceed light speed to do that in the fashion described here). This whole thing seems premised on the notion that going faster than light speed absolutely entails backwards time travel but an object with mass cannot go that fast. So how is our van Stockum Cylinder Orbiting Chrononaut managing time travel here?

Regarding an object appearing to exceed the speed of light to an observer, this may be the phenomena that Kiku was referring to.

Whack- a-Mole, IANAP but I think the time travel occurs because of the warping of space-time by the large gravitational field created by the super-dense cylinder. See, for example, the second paragraph here. Admittedly, it’s not much of a cite, but it explains the idea.

Thanks but I have to wonder about that cite.

Where is the ‘end’ of an infinitely long cylinder? Or, how do you find the middle of an infinitley long cylinder (actaullay easily for this one I suppose as any point might be considered the ‘middle’ but at best the notion is…odd).

Also, I don’t understand how you roll any mass into an infinite cylinder. 10x the mass of the sun? That’s nothing just stretched across the galaxy much less infinitely.

I’m missing something big here because none of it makes sense to me. I realize that the whole notion is a stretch but even accepting some large leaps of faith I’m still not getting it.

I agree with you about the idea of an infinitely long cylinder having “ends”. I think the writer got confused somewhere. About rolling an infinite cylinder: Keep in mind that this is purely a theoretical idea. The math shows that if you could do it then you could travel in time. If you create a cylinder that is infinitely dense (which, I think, implies a diameter of zero) then it would be infinitely long. The point is that if you plug some ridiculous, unachievable values into the equation it shows that the result is a time machine. Basically, GIGO (Garbage In, Garbage Out).