Wormholes, Warp Drives and Time Machines - Part I

Just a quickie, just putting a marker down, a public reminder to do this all better another time.

Don't get me wrong: I would love it if there were such things as traversable wormholes, faster-than-light travel and any way of getting the better of currency fluctuations (such as by going back 12 months and transferring all the money I didn't think I'd need then) but...

It's a big but, and unusually (for this type of casual blog-musing) it's predicated on the idea that Einstein was right... and the "but" in question is...

I don't think so.

Let's do the easy one first: Warp Drive - particularly the Alcubierre drive. The Alcubierre drive is a lovely idea, perfectly in keeping with the idea of a Warp Drive because it does exactly what it says on the tin, it warps space(time). In front, it squeezes it up, behind it stretches it out. But unlike the fictional drive of Zefram Cochrane it's "real" in the sense that it's not just a load of hand-waving and muttering - there's serious maths at work for the Alcubierre drive, which modifies spacetime distances by tinkering with the "metric" - that function of spacetime that says how far apart things are.

This so called metric-engineering is neat and, if one puts aside the "minor problems" ahem of the energy requirements, dealing with incoming photons etc. (apparently another metric tweak will deal with them though) and how one gets into or out of the "warp bubble", it is very, very straightforward: as many light years as you want in front get squeezed up into as little as you'd like, across which you can then wander at local sub-light speed and still arrive rather quicker than going through the "unsqueezed space".

My problem is this: how does the metric modification propagate? Surely it can't move forward faster than light? So, whilst you could bring Alpha Centuauri as near to your backyard as you might like (and then step across the picket fence in the twinkling of an eye) I can't help thinking it's going to take ~4 years to get there.

And on a practical note, what about all the Stuff between here and there? Pile it all up (not forgetting perhaps the Cosmic Microwave Background radiation in addition to bits of real, solid stuff - large and small) and I can't help wondering what it will do to metric on its own.

However, the basic issue - you can't exceed the speed of light in spacetime - remains.

The problems with Wormholes and Time-Machines are related... but that'll have to wait for Part Deux (but in a nutshell: how do you move a wormhole without squeezing and stretching space like the Alcubierre drive (there might be a way - with interesting consequences for time-machine (non) creation - give it a twist... Kerr Metric like), and how in the name of X can Lorentz transformations/boosts be applied to spacetime itself rather than separations within spacetime - i.e. how does time-dilation apply to a moving wormhole mouth? NOT!)

During the interval, if you can explain the fault in the reasoning re the Alcubierre drive above, and how metric modifications propagate FTL do let me know... it will save me making an ass of myself twice (or at least, one more time than I'm going to anyway).

Remember! Einstein was right! (and even if we improve on him, Special/General Relativity will always be suitable approximations for some things..., just as Newtonian gravity still is)

Boldly taking Stuff where no Stuff has gone before.

Enough!