rajama

Wasn't it's use a requirement at some point for military systems or did that all go away / never work out?

Oh My Goodness a computer simulation... I might actually understand 1/2 of the topic! Many thanks Ray

Okay if I 'but-in' here? Here's another 'wrinkle': a few weeks ago I was given a hand written note by a specialist to pass to my GP suggesting I try a particular drug. I could read the note' date=' but [b']not [/b] the drug name. Obviously, the scribble would have made sense to my GP within the context of the note. This suggests that the specialist had prescribed the drug so often it had reduced to scrawl, but that his normal handwriting was acceptable. Thankfully my GPs prescriptions are generated and printed by computer, so at least some progress is being made (here). Is this a general move to printed prescriptions (UK)

Martin can I ask where I would find an overview of the 'new approach' you mentioned, or maybe what search terms would provide relevent hits?

From our perspective, a tachyon's rest mass is an imaginary quantity... but to a tachyon it isn't: in it's own reference frame it would be real, wouldn't it? Just like it's speed relative to other tachyons would always be less than C..? I'm not overly familiar with GR either - I have a number of dusty text books - but you seem to be asking whether the mass of a particle following a space-like trajectory contributes to (observable) spacetime curvature..? I'm going to go with (tosses coin) yes ... er, is that thunder in the distance??

When I was a teenager I drew mazes by hand when I was bored. Years later, I would draw them to relax (zen maze drawing anyone?) and eventually made an MS Word template to make printable mazes. Okay, so here's a shot of one from about five years ago (I can't find the template right now). Have fun.

Is this kind of puzzle common - I don't usually solve puzzles... But it was weird - there was a continual conflict going on while my mind went thru all kinds of analytical solutions, something was nagging at the edge, something intangible, obviously a pattern recognition process from 'the other side', telling me I was missing something. I actually got it right several times before I knew why...

Couldn't agree more...

Their positions must coincide at time t2, so using x = vt + 0.5at^2: p1 will move to x = ut2-0.5gt2^2 & p2 will move to x = u(t2-t)-0.5g(t2-t)^2 = ut2 - ut - 0.5g(t2^2 + t^2 - 2tt2) equating these and canceling terms: 0 = u/g + 0.5t - t2 or t2 = 0.5t + u/g

Oh yes - sorry, you meant what if light were to travel at a speed in a vacuum infinitesimally close to, but not at c, due to - er - some other property of the vacuum..? I only addressed: Apologies.

Isn't there always going to be a reference frame for which you (your ship?) is moving past at walking pace - say, for someone who just stepped out the back, for instance... ...or when you say 'all reference frames' do you mean the sub-set which - I would assume, I may be wrong - are occupied by most matter in the universe? I may be entirely off here...

I really should have researched a little more before posting this thread (sorry) - I just found a handful of references to an 'entanglement laser' as a research topic at Grenoble: http://www-lsp.ujf-grenoble.fr/eng/recherche/a1t4/a1t4a3/theory.htm The related paper is available for purchase at: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000005053601000001&idtype=cvips&gifs=yes Okay, so its a down-converter in a laser cavity type thingy? I don't have access to the paper, so... It may exploit the process described here (at a guess): http://physicsweb.org/articles/news/5/8/20 This was all some time ago, so if no one has read anything elsewhere, I would guess it's still a 'work in progress'.

I assume you're talking about the Scully and Drühl Experiment - haven't read it fully yet, but it seems to be pretty similar to your proposal... Hey, there's an awful lot to read about this from Google! (duh) Thanks for the pointer...

...and doing the math won't show that? Oddly, right now I don't know if I really care if it works or not. I like to think that people are exploring these kinds of puzzles, but I imagine that - mostly - they're not. I don't like pictures of devices, in general. The diagram I drew removes the down converters, leaving only one photon to detect and an interference pattern at both ends. To me, your experiment is like simultaniously blocking two adjacent slits in my drawing, which obviously kills interference on both sides. So, we're left only with the devices: the down converters... Does it make a difference that you know, even without measuring, that two photons can never arrive simultaniously at one side? Does this prevent interference? I didn't think it did, but...

Okay. It's just that in re-reading the papers I've looked at recently, the down converter seems to be there, in many respects, to provide the degree of control over the experiment to allow the coincidence detectors to be effective. It all appears to be about painstakingly careful control - which may be something you wouldn't have a chance in achieving with the output of a laser..? But wouldn't it be useful...

Yes. I got that. I was comparing the laser and the downconverter and what I perceived as the broad similarity of the processes occuring in each. Wouldn't the difficulty in disinguishing between laser photons lead to any form of entanglement?

Did that work? You may need square brackets around each column name...

Er, yes I understood that already (pictures!), but - oh, never mind... I drew the diagram to put things in the 'traditional' context of a diffraction experiment - thought it would clarify the question of whether an interference pattern would form or not. I stared at it and it looks okay (edit: but what would I know?), so you may have a (very worrying) winner. Most of the time, however, I'm aware that everyone is wrong about this kind of thing [QM without supporting math], so I think someone will have to do the math... with matrices and everything. Volenteers?

Wow - drop shadows and everything. I know it may be a property of the diagram rather than the experiment, the top half looks a little like the usual EPR set-up, while the bottom half is a reference path to compare against. And..?

Okay, but that doesn't mean there's no entanglement - the paper I mentioned (which is at about my level, though I've forgotten most of it already) is this pdf See B. The Crystal, para 2 - the down converter produces parallel polarization in the output photons...

Is laser light always polarised or is it a matter of degree or design? Ummm - I'll go check... What about other kinds entanglement, maybe caused by the cavity?

hohoho... omg - the second reference goes on forrrrrreverrrrrrr...

I did wonder, but - okay, suddenly everything is very clear... and bright. That's why you can't move the down-converters! I'll be back...