# The Mallett Time Machine

1. Sep 12, 2004

### Ivan Seeking

Staff Emeritus
http://www.physics.uconn.edu/~mallett/ [Broken]

Does anyone know the latest on this?

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2. Sep 12, 2004

### Ivan Seeking

Staff Emeritus
3. Sep 12, 2004

### gonzo

I have a different view on early time travel, that this reminds me of. Not the exact mechanics, but the first use if a mechanic ever becomes even partially feasable.

Most of what I've seen dwells on sending large objects through time. I've seen theoretical calculations for using negative energy to keep a wormhole open, but then it is pointed out the absurd amount of energy it would take to open even the tiniest of holes, even if it was possible.

It seems to me the initial best use would be to send a single photon a very very very short distance backwards in time. You would then have in effect a compute that could perform infinite calculations instantly. Though it does seem like it would get quite hot or require a lot of energy or something.

Just a thought anyway.

4. Sep 12, 2004

### Staff: Mentor

I posted this back in April. You don't ever read my posts.

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5. Sep 12, 2004

### pervect

Staff Emeritus
I'm rather skeptical about Mallet's time machine.

The basic problem is this - the purported time machine doesn't have the regions of negative energy density that one needs, for instance, to form a wormhole, so there are theorems that suggest that Mallet's scheme should not work. I would tend to believe that Mallet probably made too many simplifications in his strong field analysis (ignoring the stress-energy tensor of the mirrors needed to make the light beam swirl would be my guess).

To quote from Steve Carlip on spr

msg id: <aa1iho$3oa$1@woodrow.ucdavis.edu>

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6. Sep 12, 2004

### sol2

Scepticism is always good eh?

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7. Sep 13, 2004

### Ivan Seeking

Staff Emeritus

I was just too busy to follow up at the time. He seems to be gaining support.

8. Sep 13, 2004

### pervect

Staff Emeritus
I don't know, is it?

To amplify on my point a bit:

http://prola.aps.org/abstract/PRD/v46/i2/p603_1

Given that Mallett's time machine is finite, Hawking's theorem would seem to apply. It's difficult to see how Mallett's result can be correct unless Hawking's result is in error, unless there is a violation of the weak energy condition. But Mallett doesn't mention any violation of the weak energy condition, there's certainly nothing that should violate it in a cylinder of rotating light. So I have to remain extremely skeptical unless I see this point addressed. BTW, the link you quoted for Mallet's paper doesn't work - and a link to his strong field analysis would be more interesting than the weak field analysis, anyway.

http://arxiv.org/PS_cache/gr-qc/pdf/0204/0204022.pdf [Broken]

has some more info on chronology protection. The second part of Hawking's analysis, the part about infinite stress-energy tensors at the CTC, may be open to challenge with a quantum analysis and some rather special conditoins (see the above URL) but nobody's challenged the first part of his analysis that I've seen.

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9. Sep 13, 2004

### Ivan Seeking

Staff Emeritus
Okay, I think I know what Mallett is using to ditch this argument: The Many Worlds Theory.

Does this sound right; not the theory, but using the MWT to escape this issue of Chronology Protection? In the audio presentation in my first link, right at the end he takes a question and uses the MWT to provide an answer.

10. Sep 13, 2004

### Staff: Mentor

The TV show had an interview with David Deutsch, so you may be correct.

11. Sep 13, 2004

### Ivan Seeking

Staff Emeritus
So, if this is correct, might this qualify as a test of the MWT? That would be interesting in itself.

12. Sep 13, 2004

### PRodQuanta

How do you figure Ivan? You've got my attention. Maybe a link. Or just your thoughts.

13. Sep 13, 2004

### Staff: Mentor

There was an article in Scientific American, March, 2004 "The Quantum Physics of Time Travel" with Deutsch. I haven't read it, but he discusses CTCs - Closed Timelike Curves

There is a paper by Deutsch

"Quantum Mechanics Near Closed Timelike Curves", Physical Review D, Vol.
44 No 10, pp 3197-3217, November 15, 1991.

I won't even pretend to understand this stuff. Just enough sinks in so that I have no clue what is being discussed.

But I've been reading "Fabric of Reality" because I think Deutsch is cute.

What is your opinion on Deutsch?

14. Sep 13, 2004

### elkoweb

John titor said that a time machine would be invented by 2007 if i remember correctly. hmmmm

15. Sep 13, 2004

### humanino

I don't understand : how the linearized approximation can be valid with a strong field ?

I also a agree with pervect : the positivity conditions of Penrose and Hawking should prevent storage of negative energy.

I totally agree with the fact that one cannot go back further than the lightcone defined by the event where the machine is switched on. This is always the case in what I have read. Besides, I wish time machine could be constructed, but I think scepticism is always the natural first reaction of a scientist.

There is a poll right now on the interpretations of QM. If you backup MWT, please vote. They need your help right now, Niel's up ahead

________
EDIT : sorry, forget the first question

Last edited: Sep 13, 2004
16. Sep 13, 2004

### Ivan Seeking

Staff Emeritus
He has been one of my favorites ever since he proved the existance of crop cylinders; finally putting the "cylinder nuts" in the mainstream.

http://www.qubit.org/people/david/UFO/UFO.html

Something else of interest that popped up while I was looking:
http://xxx.lanl.gov/abs/gr-qc/9905084

I'm confused on this point. His paper only addresses weak fields.

Last edited: Sep 13, 2004
17. Sep 14, 2004

### Staff: Mentor

Last edited: Sep 14, 2004
18. Sep 14, 2004

### Staff: Mentor

I really felt Mallett may be onto something. I am disppointed I haven't been able to find more recent information on how things are going. I was afraid that we might not have the ability to create the right conditions. I wish you could have seen the show, it went into a lot of detail.

19. Sep 14, 2004

### Ivan Seeking

Staff Emeritus
I'm just connecting the dots.

Here is more interesting information.

http://philsci-archive.pitt.edu/archive/00000845/00/TTdraft.pdf [Broken]

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20. Sep 14, 2004

### Ivan Seeking

Staff Emeritus
I'm trying to contact him. He may have something to say.

I just saw the show. Its running again on The Science Channel. It wasn't clear to me that Deutsch addressed any of these issues.