Saturday, June 28, 2008

Alice and Bob

Alice: You are late. How was your day?

Bob: Sorry honey, I had to wait for t = infinity, it took forever.

Alice: Thanks for asking, my day was perfect, I was thrown into the black hole three times.

Bob: At least you get to see something, you never tell me...

Alice: You know I can't.

Bob: What am I supposed to wear?

Alice: I took out the black suit and the shirt, it's in the bedroom.

Bob: I really hope they get this information loss stuff sorted out at some point, it's terribly annoying.

Alice: I hear we'll be back to Special Relativity next week.

Bob: Oh, really? The simultaneity again? How long will it take until they've understood it!

Alice: No, something about the clicks of the Unruh detector.

Bob: Humm. Am I supposed to wear a tie?

Alice: Well, I think the family would appreciate if you'd show some respect for my ex.

Cat: Meeow.

Bob: Oh no. Did they send more packages?

Alice: Oh yes. Seems you got the dead one, I left it downstairs.

Bob: Doesn't it ever cross their mind that disposing all these dead cats isn't so easy? The neighbors already talk, I heard them last week...

Alice: You can't wear sneakers to a funeral.

Bob: Well, he doesn't care any longer, does he?

Alice: Do me the favor, it's a tragic story and I don't want anybody to think we're not serious.

Bob: Tragic? Well, he shouldn't have shot his grandfather!

Alice: We don't even know that. Do we really have to go through this again?

Bob: Well, if we'd know whether he made it to the other side of the wormhole, you must know...

Alice: You know I can't tell you!

Bob: Yah yah! Cosmic cencorship! But it's unproved!

Alice: Well, one never knows, I don't want to cause us problems. Don't you see I'm just doing this for us!

Bob: Anyway. Will Fido be there?

Alice: Don't think so. Last time we talked he had a problem with a Kerr-Newman black hole.

Bob: Good, good. Let's go. I really think we could need a vacation.

Alice: We could ask for a different branch of the multiverse tomorrow.

Cat: Meeow.

16 comments:

Phil Warnell said...

Hi Bee,

Can we take it that the terms Alice and Bob could be substituted with Bee and Stefan? I imagine a nosy eavesdropping neighbor listening to all this. Be careful for she may have called for those fellows with the nets and strange jackets already:-)

Best,

Phil

Bee said...

Ah, no, there are no cats in our household, neither dead nor alive ones. That dialogue was inspired by a collection of short stories I read recently "Will you please be quiet, please" by Raymond Carver. Lots of unhappy couples in there, but brilliantly written. Very recommendable. Best,

B.

Phil Warnell said...

Hi Bee,

"Ah, no, there are no cats in our household, neither dead nor alive ones. That dialogue was inspired by a collection of short stories I read recently "Will you please be quiet, please" by Raymond Carver. Lots of unhappy couples in there, but brilliantly written. Very recommendable."

That’s a relief and I can understand having no cats in the premises. They could be considered at risk in a household with two physicists :-) The book you mention sounds interesting and could provide some reflective amusement.

In so saying I have to admit when I come home late some evenings to turning the radio to a program called “Coast to Coast”. It’s a talk show where all the far out people come on to discuss what I would call the wacko ideas like conspiracy of the Lumenarty, big foot, alien abductions and so forth. As it happens this past Wednesday they had a fellow on that claimed to have to developed a technique were one could peer into alternative realities and fine one more to your liking if your present one was giving you a problem. I believe I think he called it “channeling” or some such.

Anyway in as they also have a call in part where you can speak to the featured quest I was briefly tempted to call. What I wanted to relay is that the listeners could spare themselves all the expense of the for sale material and just take Telmark’s advise and simply keep shooting themselves in the head until the desired reality found:-) Anyway I often find it all quite amusing and at the same time a little concerning as I imagine many listen in for reasons other then my own.

Best,

Phil

P.S. Oh yes our Walter from stop the LHC fame was once a honoured guest of the program :-)

Phil Warnell said...

Hi Bee,

Sorry that should have been Tegmark not Telmark, just in case there is such a physicist in this or another world:-)

Best,

Phil

J. Random said...

You know, that conversation reads just as funny backwards as forwards...

stefan said...

You know, that conversation reads just as funny backwards as forwards...

Time reversal symmetry! One more physics concept hidden between the lines ;-)

Great dialogue, Bee! I guess the editor in charge of the Futures Column of Nature Physics should contact you.

Cheers, Stefan

Andrew Thomas said...

Someone had to look it up on Wikipedia: "Alice and Bob. Generally, Alice wants to send a message to Bob. These names were used by Ron Rivest in the 1978 Communications of the ACM article presenting the RSA cryptosystem, and in A Method for Obtaining Digital Signatures and Public-Key Cryptosystems published April 4, 1977, revised September 1, 1977 as technical Memo LCS/TM82. Rivest denies that these names have any relation to the 1969 movie Bob & Carol & Ted & Alice as occasionally suggested by others."

Neil' said...

So this is making me think: You are circling to the question, what if one entangled particle/photon fell into a BH and the other one didn't. We measure the outside one, and then "know" what the other one is supposed to be measured as, does that violate any "no hair" or other information destruction theorems?

Bee, get some of your cute stuff together and send it over to Discover, New Scientist, etc since you clearly have the writing talent.

Andrew Thomas said...

Neil said: "what if one entangled particle/photon fell into a BH and the other one didn't. We measure the outside one, and then "know" what the other one is supposed to be measured as, does that violate any "no hair" or other information destruction theorems?"

(are you posting in the right thread??)

The answer is no, because we're not getting information out of the hole, for the same reason that you can't use quantum entanglement for superluminal signalling (because of the random nature of quantum mechanics). You can't use quantum entanglement to transmit information.

Andrew Thomas said...

But the fact that those emitted photons remain entangled with particles inside the hole just makes me think ... hmmm ... suspicious ...

Andrew Thomas said...

Though that in itself is not the information loss paradox (have to say that to make Bee happy), it does show how the quantum realm can form a bridge between the interior and exterior of the hole.

Bee said...

Hi Andrew,

Yeah, indeed I'm happy :-) The reason that you have this 'bridge' between the in- and outside is that in quantum mechanics the collapse of the wave-function is non-local. But as we know, you can't use it to submit information, so it doesn't help. A non-local interaction however (i.e. one with which you could submit information) would be an option to avoid the information loss problem. The question is then how the details look like, and how you make sure this non-locality doesn't affect other observables since black hole formation can take place at arbitrarily low energy densities (or curvature rspt). Best,

B.

Quantum_Ranger said...

Hey Andrew have you not heard of "The use of entangled light to illuminate objects is shown to provide significant enhancements over unentangled light for detecting and imaging those objects in the presence of high levels of noise and loss. "
via quantum ranging of Seth Lloyd
http://arxiv.org/abs/0803.2022

Andrew Thomas said...

Thanks, I had a look at the paper. Very interesting. But it's not a case of sending information via quantum entanglement (ie., faster than light), it's just an example of how to use entanglement to increase signal-to-noise ratio of illuminating photons. If you find a paper on how to transmit information faster than light, let me know.

By coincidence, Alice and Bob feature here as well:

http://en.wikipedia.org/wiki/No-communication_theorem

Andrew Thomas said...

This is a fun link:

Is Faster-Than-Light Communication or Travel Possible?

Quantum_Ranger said...

Iam certain, as certain as very probable, that this post by Bee relates to the stretching of Time, and information being "mixed" in transit? So some of A's questions are answered at infrequent times!

Infalling 'input' information will collide and mix with outfalling 'output'..thus anything that has crossed an horizon, will be effectively part of an entangled "looped-space-time" ?