The White Lily (![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png)
thewhitelily) wrote2006-10-31 03:21 pm
thewhitelily) wrote2006-10-31 03:21 pm
Quantum Noodleturningness, Part One: Physical Plausibilities
I’d like to talk for a while about the plausibility of the sci-fi aspect of my NaNovel.
Feel free to tune out, because really I’m just talking to myself to try to sort this out in my brain, so it'll properly flow out my fingers in November. Most people who’ve betaed for me – but particularly Gus – will recognise this process of mine. I almost maxed out poor Gus’s gmail account with the number of lengthy essays I sent him on various subjects during the process of writing His Son’s Father. I’m only really posting it because I think it’s totally cool, and also mostly non-spoilery. And people might be interested. *shrug*
The basis of my NaNo story is a New Scientist article I read, which seemed to imply that a plausible, if unlikely, interpretation of a certain quantum quirk was that it may be possible to send messages back through time. Thanks to my physicist friend, I understand the quantumness behind this a little bit more, as well as having a context to put it all in as far as interpretation’s concerned. But I’ll talk about more of that side of things in Part Two.
The way New Scientist proposed this idea was to conceive an experiment where a laser is split, forcing two quantum entangled photons to follow different paths—one of them longer than the other, thanks to a long coil of fibre-optic cable—making an observation as to whether the photon which arrived at its destination first is behaving as a particle or a wave, and then choosing to measure the photon which arrived at its destination second as either a particle or a wave.
Since the photons are entangled, they must necessarily appear in the same form as one another. Thus, your choice as how to measure the second photon makes a difference as to how the first photon appears. And thus, it may be possible to pass information backwards in time. QED.
Obviously it’s more complicated than that, particularly since I’ve been informed by a reliable source that the predicted possible outcome for this experiment may break a number of the laws that physics has laid down for our guidance [/Oscar Wilde]. But it’s an interesting thought experiment, nonetheless, and it started my plot to hopping rather energetically, because hey - I'm writing science fiction, not actually building the darn thing.
The experiment described in New Scientist, of course, all happens on a miniscule scale. It involved a ten km length of fibre-optic cable, making the time difference in this experiment in the realm of 33 microseconds. Extrapolating (and rounding shamelessly), the length of fibre-optic cable involved in sending a message back by:
1 minute = 20,000,000 km
1 hour = 1,000,000,000 km
1 day = 26,000,000,000 km
1 week = 180,000,000,000 km
1 year = 10,000,000,000,000 km
Yes, that’s right. To send a message one year into the past, you would need almost ten trillion kilometres — that is, one light-year — of fibre-optic cable. Which, to put it rather mildly, is an extremely long cable.
So how the heck much room would it take up, even carefully coiled so it could be used?
A typical single-mode glass fibre-optic cable, including cladding, is 400 micrometers in diameter. Since the core’s only something like 5-10 micrometers, let’s say advancements in technology could cut the size down to 50 micrometers by the time my fic is set. Then let’s coil it around something big… I don’t know, let’s say something approximately the same size as the Melbourne Cricket Ground. With an approximate circumference of 500m, we would need 350,000,000,000 times around something of that size, which if coiled precisely at 50 micrometers would end up at 17,000km long.
Okay, that’s a bit big to be practical. But of course, we don’t have to wrap it in a single layer around something large. Since I can’t be bothered looking up an equation for a spiral, why don’t we, instead, wrap it around something small until it gets out to twice the diameter of the MCG. Then the average circumference should be approximately the same. At 50 micrometers apart, that gives us 3,230,000 layers. Which makes this big bloody coil of cable just over 100m high instead. Something that’s actually… dare I say it… approaching reasonable. At least, reasonable as far as the board of my megalomaniac corporation are concerned.
The other thing to take into consideration about this, is that in doing this rough calculation, I’m doing something in the league of a 50s sci-fi writer, trying to predict the size of future computers based on the size of current transistors. Meet: the integrated circuit. Absolute gold. And totally unpredictable. Still, I don’t mind so much if they’re big - I want these things to be enormous, unwieldy pimples on the face of the Earth, preferably visible from space. Or possibly actually in space. Then I’d really feel like I was writing sci-fi.
Of course, constructing these things is a big problem. But hey, they're not meant to be cheap, and they're certainly not meant to be easy, which means I think I'm okay.
But probably the most important problem I’ve got as far as the physical reality of sizing up this experiment is concerned is: how the heck do I keep the attenuation (that is, the decrease in intensity due to absorption or scattering of photons along the way) down? Glass has a lower attenuation than plastic – but there’s no way you’re going to get zero attenuation without passing the light through a total vacuum. Which makes for the biggest problem I have. Current commercially available hardware can apparently communicate reliably over something like 60km of fibre-optic cable. What that means about how much of the signal is remaining after that distance, I’m not sure.
Because, you see, I suspect that I need zero attenuation. Or at least very-low-percentage attenuation. Because the whole thing only works (or not-really-but-plausibly-maybe-works) because the photons we measure early do the same thing as the photons at the other end. If only a few of the photons actually make it through to the other end to be affected by the second sensor, it doesn’t feel right to me at all to imagine that they could affect so many more of the photons at the other end that don’t have entangled partners.
The closest thing I can think of, really, is a particle accelerator, in which I can make single photons zoom around in a vacuum for some unspecified length of time. But that doesn’t work, because, as far as I’m aware, they only really work with charged particles. In fact, I’m fairly certain that the idea of sending them through a vacuum is pretty much useless, unless I try to slingshot my photons around a black hole (or, it's been pointed out to me, bounce them off a giant space mirror) which brings a whole host more calculation problems that I don’t want to even start thinking about.
Anyone have any ideas, or shall I just make myself some Magical!Futuristic!Ultra!High!Tech!Attenuationless!Glass? Or just gloss over it?
I must admit, glossing’s looking attractive, at the moment. :)
Next up, Part Two: Interpretational Implications (or: A most ingenious paradox!)
Edit: Stop press! Apparently, in certain gasses and at certain temperatures, the speed of light can be slowed down by a significant amount - enough to make it possible to make a photon cross a room at a slow enough pace to make this work. If this is the case - and it doesn't result in a high attenuation along the way - this looks like the go. Yay! Thanks, Geoff!
Feel free to tune out, because really I’m just talking to myself to try to sort this out in my brain, so it'll properly flow out my fingers in November. Most people who’ve betaed for me – but particularly Gus – will recognise this process of mine. I almost maxed out poor Gus’s gmail account with the number of lengthy essays I sent him on various subjects during the process of writing His Son’s Father. I’m only really posting it because I think it’s totally cool, and also mostly non-spoilery. And people might be interested. *shrug*
The basis of my NaNo story is a New Scientist article I read, which seemed to imply that a plausible, if unlikely, interpretation of a certain quantum quirk was that it may be possible to send messages back through time. Thanks to my physicist friend, I understand the quantumness behind this a little bit more, as well as having a context to put it all in as far as interpretation’s concerned. But I’ll talk about more of that side of things in Part Two.
The way New Scientist proposed this idea was to conceive an experiment where a laser is split, forcing two quantum entangled photons to follow different paths—one of them longer than the other, thanks to a long coil of fibre-optic cable—making an observation as to whether the photon which arrived at its destination first is behaving as a particle or a wave, and then choosing to measure the photon which arrived at its destination second as either a particle or a wave.
Since the photons are entangled, they must necessarily appear in the same form as one another. Thus, your choice as how to measure the second photon makes a difference as to how the first photon appears. And thus, it may be possible to pass information backwards in time. QED.
Obviously it’s more complicated than that, particularly since I’ve been informed by a reliable source that the predicted possible outcome for this experiment may break a number of the laws that physics has laid down for our guidance [/Oscar Wilde]. But it’s an interesting thought experiment, nonetheless, and it started my plot to hopping rather energetically, because hey - I'm writing science fiction, not actually building the darn thing.
The experiment described in New Scientist, of course, all happens on a miniscule scale. It involved a ten km length of fibre-optic cable, making the time difference in this experiment in the realm of 33 microseconds. Extrapolating (and rounding shamelessly), the length of fibre-optic cable involved in sending a message back by:
1 minute = 20,000,000 km
1 hour = 1,000,000,000 km
1 day = 26,000,000,000 km
1 week = 180,000,000,000 km
1 year = 10,000,000,000,000 km
Yes, that’s right. To send a message one year into the past, you would need almost ten trillion kilometres — that is, one light-year — of fibre-optic cable. Which, to put it rather mildly, is an extremely long cable.
So how the heck much room would it take up, even carefully coiled so it could be used?
A typical single-mode glass fibre-optic cable, including cladding, is 400 micrometers in diameter. Since the core’s only something like 5-10 micrometers, let’s say advancements in technology could cut the size down to 50 micrometers by the time my fic is set. Then let’s coil it around something big… I don’t know, let’s say something approximately the same size as the Melbourne Cricket Ground. With an approximate circumference of 500m, we would need 350,000,000,000 times around something of that size, which if coiled precisely at 50 micrometers would end up at 17,000km long.
Okay, that’s a bit big to be practical. But of course, we don’t have to wrap it in a single layer around something large. Since I can’t be bothered looking up an equation for a spiral, why don’t we, instead, wrap it around something small until it gets out to twice the diameter of the MCG. Then the average circumference should be approximately the same. At 50 micrometers apart, that gives us 3,230,000 layers. Which makes this big bloody coil of cable just over 100m high instead. Something that’s actually… dare I say it… approaching reasonable. At least, reasonable as far as the board of my megalomaniac corporation are concerned.
The other thing to take into consideration about this, is that in doing this rough calculation, I’m doing something in the league of a 50s sci-fi writer, trying to predict the size of future computers based on the size of current transistors. Meet: the integrated circuit. Absolute gold. And totally unpredictable. Still, I don’t mind so much if they’re big - I want these things to be enormous, unwieldy pimples on the face of the Earth, preferably visible from space. Or possibly actually in space. Then I’d really feel like I was writing sci-fi.
Of course, constructing these things is a big problem. But hey, they're not meant to be cheap, and they're certainly not meant to be easy, which means I think I'm okay.
But probably the most important problem I’ve got as far as the physical reality of sizing up this experiment is concerned is: how the heck do I keep the attenuation (that is, the decrease in intensity due to absorption or scattering of photons along the way) down? Glass has a lower attenuation than plastic – but there’s no way you’re going to get zero attenuation without passing the light through a total vacuum. Which makes for the biggest problem I have. Current commercially available hardware can apparently communicate reliably over something like 60km of fibre-optic cable. What that means about how much of the signal is remaining after that distance, I’m not sure.
Because, you see, I suspect that I need zero attenuation. Or at least very-low-percentage attenuation. Because the whole thing only works (or not-really-but-plausibly-maybe-works) because the photons we measure early do the same thing as the photons at the other end. If only a few of the photons actually make it through to the other end to be affected by the second sensor, it doesn’t feel right to me at all to imagine that they could affect so many more of the photons at the other end that don’t have entangled partners.
The closest thing I can think of, really, is a particle accelerator, in which I can make single photons zoom around in a vacuum for some unspecified length of time. But that doesn’t work, because, as far as I’m aware, they only really work with charged particles. In fact, I’m fairly certain that the idea of sending them through a vacuum is pretty much useless, unless I try to slingshot my photons around a black hole (or, it's been pointed out to me, bounce them off a giant space mirror) which brings a whole host more calculation problems that I don’t want to even start thinking about.
Anyone have any ideas, or shall I just make myself some Magical!Futuristic!Ultra!High!Tech!Attenuationless!Glass? Or just gloss over it?
I must admit, glossing’s looking attractive, at the moment. :)
Next up, Part Two: Interpretational Implications (or: A most ingenious paradox!)
Edit: Stop press! Apparently, in certain gasses and at certain temperatures, the speed of light can be slowed down by a significant amount - enough to make it possible to make a photon cross a room at a slow enough pace to make this work. If this is the case - and it doesn't result in a high attenuation along the way - this looks like the go. Yay! Thanks, Geoff!
glossed glass...
I was reading (or watching) something on the more "nonsensical" results of Quantum physics recently: either Brian Greene's new book "The Fabric of the Cosmos", or the extended version of "What the Bleep: Down the Rabbit Hole". Or both. Experiments which have implied that actions we perform now can have a ripple-effect backwards through time. It's fun, fascinating stuff!
I would imagine that you cannot observe whether a single photon is behaving as a wave? Only once you observe interference patterns can you make that determination. Therefore, presumably, your message passed through time could rely on some binary code of n-second segments (depending on how much time you need to make the critical wave-or-particle determination) or even plain old Morse code?
Must go back and read that chapter again, I think! :-)
Re: glossed glass...
They sound fascinating - I haven't seen/read either of them. *puts them on list to watch out for* And absolutely, quantum is... exciting, brainscrambling stuff. Lovely, lovely.
Yes, that's right - you need a whole collection of photons before you can observe the interference pattern/lack thereof. I would imagine, however, that you could send them through fairly fast? I mean, I know they need to go through one by one, and you need a whole heap to determine the pattern, but... hmmmm, I need to do some research on how fast you send photons through a two-slit experiment. I've been imagining anything from nanoseconds up to seconds-long bursts.
Plain old morse/any kind of binary message is... difficult, as I'll go into on the one I'm writing now, because it makes the paradox situtation a whole lot harder. Also, ruling it out makes the plot a whole lot easier, which makes me happy. :)
no subject
I sat here for quite a while, trying to think of something intelligent I could add, but despite being reasonably intelligent myself, I've really got nothing. Sorry! :D
no subject
Low-attenuation glass
Which opens the door to possible misinterpretation of the message... :-)
Re: Low-attenuation glass
Say, for example, you lose 99% of your photons on the way to the other end. Each of those photons has a quantum-entangled partner that hits the photographic plate in the present - even the ones that were lost. So, 1% of those photons would have the "correct" state, whether that's wave or particle.
The other 99% hitting the plate would be... actually, I'm not sure. Is a lost photon a wave or a particle? Would they be randomly one or the other? Or would they be all waves, or all particles?
Perhaps, with the experimentally determined knowledge of whether those photons with "lost" partners register as waves/particles/random, and a cool computer that can filter out the "expected" result, that could actually work...
Yay! Thank you! *flyingtacklehug*
Also: misinterpreted message? You have no idea... *evilgrin*Re: Low-attenuation glass
:D
Re: Low-attenuation glass
Also, as far as the above thing about interference patterns goes, individual particles can interfere with themselves. There's a fairly famous experiment I can't remember the name of - but that you could find fairly easily if you're less lazy than me - that involved shooting electrons through a diffraction grating and getting interference patterns. Obviously, this was pretty suspicious for something that was supposed to be a particle, so they fired the particles through one by one.
They still got the interference pattern.
no subject
In any case, if you have trouble making it work out, remember in SF you are allowed one piece of silliness to enable the plot. Any further silliness is detracting. Like the famous quote from someone I can't remember and whom my googling skills are not good enough to find.
Re: Low-attenuation glass
One piece of silliness, eh? I'll have to keep that in mind... I may be in dire need of it later...