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Showing posts with label Time Machine. Show all posts
Showing posts with label Time Machine. Show all posts
Saturday, 15 January 2011
Wormholes & Time Machines (again)
If you want to know the answer to a tough question, ask the experts... Doing exactly that over at Physics Stackexchange. You can follow progress there.
Tuesday, 10 March 2009
No cigar
Not even close! But no surprise there.
The results of the FQXi Time Essay competition are now in and as expected the luminaries shone bright. Julian Barbour's essay won the (well deserved) first prize; Ellis and Rovelli and other recognisable names also scooped prizes but there was also recognition etc. for many other interesting submissions from researchers I was previously unfamiliar with (I particularly liked What Makes Time Special by Craig Callender)
The only downside here (well, I say the only downside... $$$ would have been handy!) is that I am still none the wiser about whether the issues I perceive with wormhole time machines are valid or not. That's actually a double-bummer really.
So... should you be a random relativist unexpectedly suckered in by a Google search for FQXi, Julian Barbour, etc. and have a few minutes to spare do feel free to disabuse me - I would be very grateful.
They do say it's the taking part that counts, but if no one can even tell you whether you completed the course...
Obviously I have unresolved issues.
[And to coin a neofranglaisism, a propos pantological science essays... "Le tat, c'est moi!"]
A bientot, Stuff Seekers!
The results of the FQXi Time Essay competition are now in and as expected the luminaries shone bright. Julian Barbour's essay won the (well deserved) first prize; Ellis and Rovelli and other recognisable names also scooped prizes but there was also recognition etc. for many other interesting submissions from researchers I was previously unfamiliar with (I particularly liked What Makes Time Special by Craig Callender)
The only downside here (well, I say the only downside... $$$ would have been handy!) is that I am still none the wiser about whether the issues I perceive with wormhole time machines are valid or not. That's actually a double-bummer really.
So... should you be a random relativist unexpectedly suckered in by a Google search for FQXi, Julian Barbour, etc. and have a few minutes to spare do feel free to disabuse me - I would be very grateful.
They do say it's the taking part that counts, but if no one can even tell you whether you completed the course...
Obviously I have unresolved issues.
[And to coin a neofranglaisism, a propos pantological science essays... "Le tat, c'est moi!"]
A bientot, Stuff Seekers!
Friday, 25 July 2008
Rocketship Dean (Wormholes, Warp Drives and Time Machines - Part II)
In anticipation of the dénouement (what a lovely word!) of the Wormhole-Time Travel thread (see Part I here), I have to describe how one is supposed to construct a time-machine using a wormhole. You may wish to follow the instructions at home...
You will need:
Ensure the Wormhole Grapple is working and grab one end of the wormhole. Wish Dean luck and launch towards Alpha Centauri at high acceleration so that he very rapidly achieves 0.999998c... At this speed, and assuming the turnaround is quick at the other end (and that he doesn't spend too long haggling for the hat) Dean will be back in what seems to be about a week by his "clock" (just enough time allow him to catch up on some report-writing...) while 8.6 years pass on Earth (but... he'll miss the deadline, won't he? Not necessarily... read on)
Yes, we see the effect of time dilation as we look out of the window at Rocket ship Dean's tail-light... it was blinking once a second before launch, now it is flashing only once every seven and a half minutes.
But wait! Dean's got the wormhole with him... let's take a peek through that! Now, the wormhole is travelling with Dean... there is no relative motion and so, according to most authorities, Dean does not appear slowed down by a factor of 450 when seen through the wormhole. That's not lethargy - it's just intense concentration!
Half way through day 3 Dean looks up and says "I'm here!", nips out, buys a hat, and sets off home again. Three and half days after that he lands. We can see through the wormhole that he is indeed back - but wait! Looking up into the sky in the general direction of Alpha Centauri we see a very, very slowly blinking light. He's still on his way there!
How can this be? Is he indeed the Kwisatz Haderach? No... he's in the future. If he should so wish though, he can step back through the wormhole and as far as friends, family and deadlines are concerned he has been away for only a week, rather than, disappearing without trace for 8.6 years (c.f. "A Quick Trip to Budapest to do some Scribbling")
Likewise, we can go the other way and step 8.6 years into the future (bring back info on the future, clean up on long term investments and the lottery etc....)
No, I'm not making this up (well, not all of it...) here's a respected Professor outlining the same thing [NB I offer this link as it's the only one I know of that has a nice story - the same underlying principles are outlined all over the place]
Well... if you thought quantum mechanics was confusing now you can try getting your head around time-travel and all the attendant paradoxes...
But wait! Is it true? Er... no... or at least I don't think so. The problems are these (and I'm actually neglecting most of the practicalities):
Firstly, relativistic effects - Special or General - apply to separations in spacetime; they do not, as far as I know apply to spacetime. In fact I can't see how they could meaningfully apply.
Secondly, the effects as described would appear to be asymmetrical and suggest that in multiply connected spacetime (that's spacetime with holes in it) most conservation laws go out the window (e.g. if Dean sends me a pencil through the wormhole what 4-momentum (energy +3-momentum) does it have???)
Thirdly, even if a wormhole can move, how does it?
...
Thirteenthly, I forgot to supply a loo for Rocketship Dean.
These and other points will be addressed in due course. Is there a way of restoring equivalence to our inertial frames even in multiply connected spacetime... perhaps - in which case, no time machine can be formed in this way.
Warped space, warped thinking... Paradoxical Stuff.
You will need:
- One Traversable Wormhole (preferably macroscopic) about 1m in length (distance between the wormhole mouths)
- One Human-rated rocket ship capable of v~c speed (with supplies and fuel and suitable shielding of course)
- One Wormhole Grapple (ah... yes... how's that work then? Dunno), to be attached to the rocket ship
- One set of Inertial Damp(en)ers - lest the pilot be squashed
- A willing friend - ideally one who likes travel, for which reason I have selected Dean as Pilot to the Stars (please bring me back a hat from Alpha Centauri...)
- [Yoghurt pots and sticky tape are not strictly necessary, but you never know...]
Ensure the Wormhole Grapple is working and grab one end of the wormhole. Wish Dean luck and launch towards Alpha Centauri at high acceleration so that he very rapidly achieves 0.999998c... At this speed, and assuming the turnaround is quick at the other end (and that he doesn't spend too long haggling for the hat) Dean will be back in what seems to be about a week by his "clock" (just enough time allow him to catch up on some report-writing...) while 8.6 years pass on Earth (but... he'll miss the deadline, won't he? Not necessarily... read on)
Yes, we see the effect of time dilation as we look out of the window at Rocket ship Dean's tail-light... it was blinking once a second before launch, now it is flashing only once every seven and a half minutes.
But wait! Dean's got the wormhole with him... let's take a peek through that! Now, the wormhole is travelling with Dean... there is no relative motion and so, according to most authorities, Dean does not appear slowed down by a factor of 450 when seen through the wormhole. That's not lethargy - it's just intense concentration!
Half way through day 3 Dean looks up and says "I'm here!", nips out, buys a hat, and sets off home again. Three and half days after that he lands. We can see through the wormhole that he is indeed back - but wait! Looking up into the sky in the general direction of Alpha Centauri we see a very, very slowly blinking light. He's still on his way there!
How can this be? Is he indeed the Kwisatz Haderach? No... he's in the future. If he should so wish though, he can step back through the wormhole and as far as friends, family and deadlines are concerned he has been away for only a week, rather than, disappearing without trace for 8.6 years (c.f. "A Quick Trip to Budapest to do some Scribbling")
Likewise, we can go the other way and step 8.6 years into the future (bring back info on the future, clean up on long term investments and the lottery etc....)
No, I'm not making this up (well, not all of it...) here's a respected Professor outlining the same thing [NB I offer this link as it's the only one I know of that has a nice story - the same underlying principles are outlined all over the place]
Well... if you thought quantum mechanics was confusing now you can try getting your head around time-travel and all the attendant paradoxes...
But wait! Is it true? Er... no... or at least I don't think so. The problems are these (and I'm actually neglecting most of the practicalities):
Firstly, relativistic effects - Special or General - apply to separations in spacetime; they do not, as far as I know apply to spacetime. In fact I can't see how they could meaningfully apply.
Secondly, the effects as described would appear to be asymmetrical and suggest that in multiply connected spacetime (that's spacetime with holes in it) most conservation laws go out the window (e.g. if Dean sends me a pencil through the wormhole what 4-momentum (energy +3-momentum) does it have???)
Thirdly, even if a wormhole can move, how does it?
...
Thirteenthly, I forgot to supply a loo for Rocketship Dean.
These and other points will be addressed in due course. Is there a way of restoring equivalence to our inertial frames even in multiply connected spacetime... perhaps - in which case, no time machine can be formed in this way.
Warped space, warped thinking... Paradoxical Stuff.
Tuesday, 22 July 2008
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!
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
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!
Tuesday, 1 July 2008
Earth Devouring Black Hole "Pure Fiction"
Are you worried about the Large Hadron Collider? Are you worried that you aren't worried about it? Should you be worried?
Think about it. If The Large Hadron Collider Produced A Microscopic Black Hole, It Probably Wouldn't Matter at least so says UC Santa Barbara Physics Professor Steve Giddings and his co-author Michelangelo Mangano of... wait for it... the European Centre for Nuclear Research (CERN - it's French) - who are about to turn the LHC!
Do I detect a conflict of interest here? Well, do I?
The idea of particle colliders producing black holes that could devour the Earth might make a good film script but according Steve Giddings, it's just "pure fiction".
Well, They would say That, wouldn't They?
(Am I getting the hang of this conspiracy style thing?)
Junk Stuff (because I can't figure out how to finish the other post on Wormhole time machines, mostly because I haven't the faintest idea how to re-write the metric for a twisted wormhole in Kerr coordinates instead of the customary Schwarzschild coordinates...)
Think about it. If The Large Hadron Collider Produced A Microscopic Black Hole, It Probably Wouldn't Matter at least so says UC Santa Barbara Physics Professor Steve Giddings and his co-author Michelangelo Mangano of... wait for it... the European Centre for Nuclear Research (CERN - it's French) - who are about to turn the LHC!
Do I detect a conflict of interest here? Well, do I?
The idea of particle colliders producing black holes that could devour the Earth might make a good film script but according Steve Giddings, it's just "pure fiction".
Well, They would say That, wouldn't They?
(Am I getting the hang of this conspiracy style thing?)
Junk Stuff (because I can't figure out how to finish the other post on Wormhole time machines, mostly because I haven't the faintest idea how to re-write the metric for a twisted wormhole in Kerr coordinates instead of the customary Schwarzschild coordinates...)
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