Ronald Mallett and his time machine.

[brettdbass]

http://www.dailymail.co.uk/pages/liv...n_page_id=1965

Mallett believes it is possible to use a series of four circulating laser light beams swirling spacetime around like "a spoon stirring milk into coffee".
If you were to walk into this 'timetunnel' - which would resemble a large vortex of light a few feet across - you could emerge at some point in the past. He thinks he can build a prototype machine in the lab, using today's technology, with funds of just $250,000 (£120,000).

I assume that a number of you will have seen or heard this guy recently as he promotes his latest book here in the UK.
So, what does everyone think?

Personally I think that the amount of energy required to send anything of any substance (ie: a dog rather than a few atoms) backwards by any serious amount (ie: a month rather than a second or two) will be so huge as to render it impossbile.
I also have issue with the source - these spinning laser beams themselves must surely be hugely powerful to enable transport of anything substantial, I would wager far more powerful than anything currently within our ability.

I don't profess any expertise, just a lifelong interest in and watching brief over pioneering physics.

The floor is yours...

[brettdbass]

And if anyone is online now and wants to know what I'm on about, he's on Radio 2 right now.

[Cuddles]

There's a thread about this here: http://forums.randi.org/showthread.php?t=90619
and a rebutal paper here:
http://arxiv.org/PS_cache/gr-qc/pdf/0410/0410078v1.pdf

Basically, it is a valid solution to the relativity equations, but can't ever be practical. There are two major problems. Firstly, the density of light required is on the order of that to form a black hole, which means even converting all the matter in the Solar System into light wouldn't be enough. Secondly, the closed timelike curves are only predicted to appear well outside the observable universe. In fact the phrase used is "so fantastically large that it cannot even be sensibly compared to the radius of the visible universe". There is also a distinct possibility that, like many other solutions to the Einstein equations, they are valid mathematically but not physically.

[brettdbass]

Thanks for the excellent, informative post Cuddles.

I wonder why such a well respected and apparently otherwise rigorous professor of science is continuing to walk down this blind alley. I know that the inspiration for his entire scientific career is a highly emotive one for him, but you would expect that after a lifetime of utilising and examinig scientific method he would be able to separate his emotions from his physics.

My inner cynic is making noises - he's saying something about money, but I can't quite hear him clearly

[Cuddles]

I think the thing is, nothing we know about the universe says time travel is impossible, and some theories even say it happens all the time on a subatomic scale. Even better, there are many valid solutions to the realtivity equations that say time travel is possible, although only in certain circumstances, often impossible to create in reality. Chasing time travel from this perspecive, rather than the crackpot building one in your basement perspective, is like a lot of other theoretical work. It doesn't mean anything now, and it's possible it will never lead to anything useful, but the possibility is there that all you need to do is play around with the equations a little bit more and it will all fall into place. It's not necessarily greed or quackery, it's often just plain old scientific curiosity.

[brettdbass]

Very good points.

It is true though that Mallett is pimping himself in the UK media with his much trumpeted claim that he could build a working time machine with an investment of only £120,000.
Combined with the obvious impracticalities/impossibilities of his current design, that's what's setting off the little voice inside for me.

Still, in the interests of progress I wish him all the best. It would certainly be amazing to witness if he proved all the critics wrong and did build one in his garage!

[vbloke]

It is true though that Mallett is pimping himself in the UK media with his much trumpeted claim that he could build a working time machine with an investment of only £120,000.

My take on it is, he could surely build it, then travel back in time to prove that it works and this proof would garner him more than the £120,000 he's asking for.

[Allo Allo]

My take on it is, he could surely build it, then travel back in time to prove that it works and this proof would garner him more than the £120,000 he's asking for.

No one would believe him anyway because it would be a subjective experience....no proof....

[FarSideOfTheMoon]

No one would believe him anyway because it would be a subjective experience....no proof....

It isn't hard to think of a control to prove he has travelled back in time.

[Allo Allo]

It isn't hard to think of a control to prove he has travelled back in time.

These might be silly questions, but IF (just IF) such a machine could be built - would someone "disappear" (like the movies)?

What kind of control might one put in place?

[brettdbass]

All this talk makes me want to read The End Of Eternity again.

[Cuddles]

These might be silly questions, but IF (just IF) such a machine could be built - would someone "disappear" (like the movies)?

It depends. If they came back to exactly the same time they left, there wouldn't be any time for them to disappear in. If they are free to travel around and come back to whenever they feel like then they would disappear and reappear somewhere else, or even not reappear and only get back by living through all the time in between.

One interesting point about many "real" time machines (that is, theoretically possible ones rather than sci-fi ones) is that it isn't usually possible to go any further back than the time the machine first became operational. I suspect this one is the same, since the closed timelike curves only exist while the lasers are there, so there is no way of going back before they were turned on.

This raises a few interesting problems. Firstly, it means time travel is basically pointless. It could be interesting as a kind of museum, where instead of storing things in a building you just store the time machine, but you can never go back and explore interesting events because the time machine didn't exist then. Another problem is that if everything that enters it emerges in the same place and time, what happens to them? Would they all merge into a big blob, or explode, or what? Another consequence of this is that you will have proof of time travel as soon as you turn it on.

What kind of control might one put in place?

The obvious control would be to bring back an object for which we have records, but no actual example. However, given the conditions above, the best idea would be to leave the problem for people to work out in the future, then they can bring the proof back when you turn the machine on.
Edit: Or just get Hobbes to do it for you.

[brettdbass]

One interesting point about many "real" time machines (that is, theoretically possible ones rather than sci-fi ones) is that it isn't usually possible to go any further back than the time the machine first became operational. I suspect this one is the same, since the closed timelike curves only exist while the lasers are there, so there is no way of going back before they were turned on.

You are absolutely correct, Cuddles.
From the original article linked...

There are several important things to realise about Mallett's time machine. For a start, it would only be possible to travel back in time to a point after the machine was first switched on.
If you turned on the machine, on January 1 say, and left it running for three months, you could enter the machine in March and only travel back as far as January 1. So no trips back to the Middle Ages or to Ancient Rome.