73 réponses à ce sujet

[abstractwhiz]

You're not coming across as totally lost - I just tossed weird math at you after all. It still confuses me a bit, and I'm never quite sure that I understand properly, which is why that course left me unsatisfied. 

I'm not quite sure I understand your question, but maybe it will make more sense if I explain what the equations mean.

My earlier example just came out of analyzing a system with two qubits. Qubits are quantum bits: they take 0 or 1 values like normal bits, but live in-between the two in quantum neverland (superposition is the technical term) until you make a measurement. At that point they wind up turning into either 0 or 1. Opinions are divided about what exactly is happening here - the Copenhagen interpretation of QM holds that the measurement causes the wavefunction to collapse, and the qubit takes one of the two states. The many-worlds interpretation holds that it becomes both 0 and 1, but each outcome takes place in a distinct parallel universe, so you only see one of them, and presumably your counterpart in the other universe sees the opposite outcome. This is actually serious physics, and as you might imagine, it's a goldmine for science fiction authors. 

Usually people identify these 0/1 values with the spin of a particle - this is a quantum number that is either 'up' or 'down', and you can assign 0 and 1 to either one of those. It doesn't have to be spin though - it could be some other property. The math doesn't care, it just abstracts away those details to leave you 0 and 1, since the physical realization of the system is irrelevant.

So now if you say that the state of a single qubit is (|0> + |1>)/sqrt(2), this is the mathematical version of saying that the qubit is in a 50-50 superposition between 0 and 1. If you measure it, the spin will be up half the time, and down the other half of the time. A simpler case is if the state is just |0> - then you'll always get the same measurement 100% of the time. 

Now if we take both these qubits as a single system, the state of the entire system is described by the tensor product of the two component states: |0>(|0> + |1>)/sqrt(2), which can also be written as (|00> + |01>)/sqrt(2). If something like this pops out at the end of your analysis of some fancy two-qubit system, then you know you have two qubits where the first is always 0, and the other is 0 half the time, and 1 otherwise. If you look at the version where I multiplied it out, it's basically saying that half the time you have (0, 0), and the other half you have (0, 1). Slightly different way of looking at the same thing, but you see that you can separate the two qubits. They don't imply anything about each other's states - the first one is always 0, regardless of the other guy, which is basically just a coin toss. In other words, you can decompose the system, or 'disentangle' it, if you prefer. 

On the other hand, if your analysis produces something like (|00> + |11>)/sqrt(2), it's saying that you have (0, 0) half the time, and (1, 1) the other half. Notice now that you can't decompose the state. If the first qubit is 1, the second has to be 1 as well. The system is unable to produce any states where the two bits have different values. Because knowing one bit instantly gives you the value of the other, without having to bother with the actual measurement, you've got entanglement. 

Hopefully I remember this right, or maybe a real physicist will turn up and "laugh the blue off my ass". 

Modifié par abstractwhiz, 11 avril 2010 - 07:51 .

[GnusmasTHX]

Cool.



Because I totally needed one... Oh wait.

[cindercatz]

AbstractWhiz

Ahh, now I see. Thank ya very much. :-) So, the reason we'd expect gobbledygook on the recieving end is that we can't really predict which state a qubit will take when it takes particle form (from our perspective, as particles also exist in waveform) when we observe it, only that it has become entangled as we observe it over multiple instances, so that would actually make it quite difficult to read regardless of assigned language. So my new questions would be, knowing for instance that we can slow down a photon enough to observe directly (by running it through neon gas filled tubes or something like that, or neon plasma, big difference I know, don't remember exactly), does that unpredictability remain intact at slowed speeds, or can we lock and control an entangled particle's qubit state and thereby do the same for its partner? I believe that's the idea with quantum computers, right. to lock and control individual protons within carbon atoms? It's more complicated I know, just recalling that from I believe National Geographic a while back, or Discover, one of 'em. And just how precisely can we read any given superposition event? I know we can get a lot of math from the heavy instrumentation in the newer particle accelerators, at least from creating impacts, but collisions don't work for what we're talking about, of course.

I have seen quite a lot of Michio Kaku over the years, with the multiverse idea and the snap possibilities, etc. and I read the articles as they come out. I love this stuff. :-) I wonder if we'll get an episode of "Sci-Fi Science" about quantum entanglement.

Modifié par cindercatz, 11 avril 2010 - 11:21 .

[Dethateer]

Ryanratto wrote...

It just goes to show how much thought, effort and research goes into Biowares games.

I think mr. Ryan just invented a joke capable of dethroning Cartman's fishsticks joke.

[abstractwhiz]

cindercatz wrote...

AbstractWhiz

Ahh, now I see. Thank ya very much. :-) So, the reason we'd expect gobbledygook on the recieving end is that we can't really predict which state a qubit will take when it takes particle form (from our perspective, as particles also exist in waveform) when we observe it, only that it has become entangled as we observe it over multiple instances, so that would actually make it quite difficult to read regardless of assigned language. So my new questions would be, knowing for instance that we can slow down a photon enough to observe directly (by running it through neon gas filled tubes or something like that, or neon plasma, big difference I know, don't remember exactly), does that unpredictability remain intact at slowed speeds, or can we lock and control an entangled particle's qubit state and thereby do the same for its partner? I believe that's the idea with quantum computers, right. to lock and control individual protons within carbon atoms? It's more complicated I know, just recalling that from I believe National Geographic a while back, or Discover, one of 'em. And just how precisely can we read any given superposition event? I know we can get a lot of math from the heavy instrumentation in the newer particle accelerators, at least from creating impacts, but collisions don't work for what we're talking about, of course.

I have seen quite a lot of Michio Kaku over the years, with the multiverse idea and the snap possibilities, etc. and I read the articles as they come out. I love this stuff. :-) I wonder if we'll get an episode of "Sci-Fi Science" about quantum entanglement.

I don't really know much about the specific physics of it - I learned it from a computational perspective, with the details of the physical realization abstracted away. This is where you need a physicist. 

But I'm very surprised that people haven't heard about this stuff before. It's been popular outside of hardcore physics for at least a decade, if not more. My first reaction to the thread was an incredulous WTF, because I thought everyone knew quantum entanglement was real.  

[Explosive Personality]

ppf this reminds me why I gave up physics that many worlds theory blew my mind when I first heard it. Basically I learnt the more you study physics the crazier it gets. For example doesn't Quantum Mechanics go crazy with black holes or am i mixing that up with something else

[Lord_Tirian]

abstractwhiz wrote...


I don't really know much about the specific physics of it - I learned it from a computational perspective, with the details of the physical realization abstracted away. This is where you need a physicist. 

Well, it's pretty much the same stuff physics undergrads get to hear in their "QM 101"-courses - and it's pretty much spot on... though they don't start with the convenient Bra-Ket notation but force us to grind through that stuff in matrix notation... which is insightful, but a pain.

I'd also like to expand on *possible* uses of QE (since communication through QE is impossible) - it's not just an interesting phenomenon, it can be really, really useful: Cryptography. Entangled system give you the ability to create systems that detect eavesdropping and do other interesting stuff - but that's beyond my expertise (crypto is interesting to me... but not something I do).

[Niten Ryu]

Here's quote from Kaku's book - Physics of the Impossible (pages 62-63)

"Did information really travel faster than light? Was Einstein wrong
about the speed of light being the speed limit of the universe? Not
really. Information did travel faster than the speed of light, but the information
was random, and hence useless. You cannot send a real
message, or Morse code, via the EPR experiment even if information
is traveling faster than light.

Knowing that an electron on the other side of the universe is spinning
down is useless information. You cannot send today's stock quotations
via this method. For example, let's say that a friend always
wears one red and one green sock, in random order. Let's say you examine
one leg, and the leg has a red sock on it. Then you know, faster
than the speed of light, that the other sock is green. Information actually
traveled faster than light, but this information is useless. No signal
containing nonrandom information can be sent via this method.

For years the EPR experiment was used as an example of the resounding
victory of the quantum theory over its critics, but it was a
hollow victory with no practical consequences. Until now.

Everything changed in 1993, when scientists at IBM, led by Charles
Bennett, showed that it was physically possible to teleport objects, at
least at the atomic level, using the EPR experiment. (More precisely,
they showed that you could teleport all the information contained
within a particle.) Since then physicists have been able to teleport photons
and even entire cesium atoms. Within a few decades scientists
may be able to teleport the first DNA molecule and virus.

Quantum teleportation exploits some of the more bizarre properties
of the EPR experiment. In these teleportation experiments physicists
start with two atoms, A and C. Let's say we wish to teleport
information from atom A to atom C. We begin by introducing a third
atom, B, which starts out being entangled with C, so B and C are coherent.
Now atom A comes in contact with atom B. A scans B, so that
the information content of atom A is transferred to atom B. A and B become
entangled in the process. But since B and C were originally entangled,
the information within A has now been transferred to atom C.
In conclusion, atom A has now been teleported into atom C, that is, the
information content of A is now identical to that of C.

Notice that the information within atom A has been destroyed (so
we don't have two copies after the teleportation). This means that anyone
being hypothetically teleported would die in the process. But the
information content of his body would appear elsewhere. Notice also
that atom A did not move to the position of atom C. On the contrary, it
is the information within A (e.g., its spin and polarization) that has
been transferred to C. (This does not mean that atom A was dissolved
and then zapped to another location. It means that the information
content of atom A has been transferred to another atom, C.)"

Modifié par Niten Ryu, 11 avril 2010 - 01:46 .

[Warlokki]

Niten Ryu wrote...

Here's quote from Kaku's book - Physics of the Impossible (pages 62-63)

SNIP

Wait, one atom transports the info beetween the other two? In layman's terms.
Ain't the B atom still limited by the lightspeed limit?

[cindercatz]

Not really. You could move atom B at any time. If you then change the state of atom C (where B and C are entangled), and atom B remained entangled with atom C, then atom B should change instantly to mirror atom C. Then you entangle B with A and A = C. Atom B has to travel at ‹ or = lightspeed, but the information you wish to copy can be assigned at any time so long as atoms C and B remain entangled. That's why he's wrong about communication. Communication can be encoded, if you will, as static physical information. If you can replicate physical information, you can communicate. There's just that extra step that I have no idea why everybody overlooks. You just have to be able to reliably read that physical information. Either both things (communication and what he calls teieportation, all of which would be the same thing: QE replication) are possible, or neither are. If, on the other hand, changing the state of atom C disentangled the pair, both could still be replicated, just not FTL.

There are also serious ideas about FTL travel, btw. Supposedly, this takes an immense amount of mass, a la black holes or worm holes, used to bend space-time in a rubberband effect around a vessel, but how you would aquire or manipulate that amount of mass I have no idea. Alternatively, there's an idea that you could achieve the same effect using negative energy, since the positive universe wants to cancel it out, but it takes an immense amount of energy to aquire the smallest bit of negative energy, and then it is negated extremely quickly, so again, I don't know how we'd get there. I'm pretty sure that's where the "mass effect" thing comes from, though. They just invented the magical Element Zero to get around the known problems. ;-)

Modifié par cindercatz, 11 avril 2010 - 04:02 .

[Mycrus Ironfist]

okay for all your science types out there...



in order to beat the bad guys, the good guys will ultimately need to find different tech than the mass effect... what cool alternative tech can you guys come up with?

[cindercatz]

Anti-matter bombs? *sci-fi hat* If you can use "mass effect fields" like the do in this game, maybe it makes sense that you could suspend anti-matter, which is otherwise highly explosively, atomically destructive when contacting regular matter, in these fields and then launch the whole thing at an enemy ship or Reaper at range. If anything caused the anti-matter payload to come into contact with even the bombshell, such as a defensive mass effect field, you'd get a very large bang.

[Explosive Personality]

Well this is just a hunch of mine but Didn't EDI and Sovereign have highly sophisticated Virus'.

Who needs to fire a gun when u can just use the "turn off button". It'll be interesting to see if they expand that in ME3

[Mycrus Ironfist]

Explosive Personality wrote...

Well this is just a hunch of mine but Didn't EDI and Sovereign have highly sophisticated Virus'.
Who needs to fire a gun when u can just use the "turn off button". It'll be interesting to see if they expand that in ME3

i guess movie spoilers are okay here... was shown in terminator salvation... resistance captured a signal from skynet that would shutoff the machines... turned out to be a ruse from skynet to expose resistance HQ that was transmitting the signal from a submarine.

[Mycrus Ironfist]

cindercatz wrote...

Anti-matter bombs? *sci-fi hat* If you can use "mass effect fields" like the do in this game, maybe it makes sense that you could suspend anti-matter, which is otherwise highly explosively, atomically destructive when contacting regular matter, in these fields and then launch the whole thing at an enemy ship or Reaper at range. If anything caused the anti-matter payload to come into contact with even the bombshell, such as a defensive mass effect field, you'd get a very large bang.

me like it... i was thinking along the lines of using the mass effect in creative ways only humans can come up with to beat the baddies...

but i was more like looking for another line of tech with nothing related the mass effect.

sh*t can't speak clearly with this no spoiler allowed non-sense...

[TheUnusualSuspect]

I remember reading about a guy who was using light-refrection around QE particles to transmit information. Near as I understood it, it was possible to transmit information by examining the state at one end while under the effect of photon bombardment, and by looking at the refraction of light at the other end, it was possible to transmit information about the light striking the other end.



This was all very experimental though, and it wasn't proven if the information transfer took place at FTL speeds.



I've read about the information paradox, and for the life of me, I cannot properly comprehend how a paradox exists, because all the examples I've seen used to explain it are self-contradictory with regards to dilated time scales when observed from a third location.

[Fiery Phoenix]

Interesting talk, guys. We had a similar discussion in the Lazarus Project thread on here several weeks ago.

[Dethateer]

cindercatz wrote...

Anti-matter bombs? *sci-fi hat* If you can use "mass effect fields" like the do in this game, maybe it makes sense that you could suspend anti-matter, which is otherwise highly explosively, atomically destructive when contacting regular matter, in these fields and then launch the whole thing at an enemy ship or Reaper at range. If anything caused the anti-matter payload to come into contact with even the bombshell, such as a defensive mass effect field, you'd get a very large bang.

Erm, wouldn't it be easier to contain the antimatter magnetically combined with mass elimination from the fields?
And aren't the kinetic barriers basically energy fields?

[SuperMedbh]

The funny thing is that QE communication seems to have already turned into a science fiction meme. Put it on the shelf with solid Dyson Spheres and learning via RNA injections: things that would never actually work in real life, but are too much fun not to in SF.



Cap'n, the ship, she canna go any faster, the drive core is out of handwavium!

[JohannRSA]

Dethateer wrote...

cindercatz wrote...

Anti-matter bombs? *sci-fi hat* If you can use "mass effect fields" like the do in this game, maybe it makes sense that you could suspend anti-matter, which is otherwise highly explosively, atomically destructive when contacting regular matter, in these fields and then launch the whole thing at an enemy ship or Reaper at range. If anything caused the anti-matter payload to come into contact with even the bombshell, such as a defensive mass effect field, you'd get a very large bang.

Erm, wouldn't it be easier to contain the antimatter magnetically combined with mass elimination from the fields?
And aren't the kinetic barriers basically energy fields?

Yes you are correct. Magnetic fields can also suspend plasma so it does not melt its containment unit.
You can use super magnetic field generators to suspend organic matter as well. On Discovery they had a frog suspended in midair inside a very strong magnetic field generator.

Modifié par JohannRSA, 12 avril 2010 - 08:08 .

[zach626]

sorrowandsadness wrote...

So, Schrödinger's cat walks into a bar. And doesn't.

http://xkcd.com/45/

[WarAxe7]

Just to recap a bit because I've been away (the weather was too gorgeous to think about QE)...



...in theory a quantum entangled particle pair could be separated by any distance within our space-time and still share a state. Information could be transmitted, although you'd have to figure out a protocol to allow for only one-way transmit at any point in time... the same way on a speaker phone you can't both be listening to the other side and talking to the other side at the same time.



I know that beaks the "rule" about FTL information... and it bugs me, but the math is solid, and it just needs an ENGINEER to make it happen. Us engineers have been making the gobbledygook inside scientists' heads usable for the real world since the beginning. :-)



And don't forget... we're still trying to figure out what happens to information captured in a black hole and evaporated out ("sort of"). Many many questions are asked the farther from Newtonian physics you wander.

[TheUnusualSuspect]

WarAxe7 wrote...

...in theory a quantum entangled particle pair could be separated by any distance within our space-time and still share a state. Information could be transmitted, although you'd have to figure out a protocol to allow for only one-way transmit at any point in time... the same way on a speaker phone you can't both be listening to the other side and talking to the other side at the same time.

Easy fix.  Have 2 x QE pairs, each is a one-way channel in the opposite direction to the other.

[TheUnusualSuspect]

WarAxe7 wrote...

And don't forget... we're still trying to figure out what happens to information captured in a black hole and evaporated out ("sort of"). Many many questions are asked the farther from Newtonian physics you wander.

I'm partial to the quantum fuzzball theory myself.  The thought of a true infinite density / zero size singularity does not sit well with me at all.

Fuzzball Theory

Modifié par TheUnusualSuspect, 12 avril 2010 - 10:08 .