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Physicists Create Quantum Link Between Photons That Don't Exist At the Same Time
sciencehabit writes "Physicists have long known that quantum mechanics allows for a subtle connection between quantum particles called entanglement, in which measuring one particle can instantly set the otherwise uncertain condition, or 'state,' of another particle—even if it's light years away. Now, experimenters in Israel have shown that they can entangle two photons that don't even exist at the same time. Anton Zeilinger, a physicist at the University of Vienna, says that the experiment demonstrates just how slippery the concepts of quantum mechanics are. 'It's really neat because it shows more or less that quantum events are outside our everyday notions of space and time.'"
'It's really neat because it shows more or less that quantum events are outside our everyday notions of space and time.'"
No, not really. You're simply see the macro effects of partial photons interacting, and unwilling to give up the idea of the discrete photon.
If all you can see (and measure) is a photons promotion and demotion of electrons, you an only see the fast shift of the big circles jumping around in this picture, not the slower smaller drift that is happening.
http://i.imgur.com/AUXb2N9.gif
Give up your photon model, it's based on a faulty understanding.
At some point, science just got too weird. We had this nice model of the universe with atoms, some laws of motion and thermodynamics. The universe was basically a giant billiards match. It made sense. It was easy to explain. Then we get into quantum mechanics and everything is crap shoot. Multiple universes. Particles that behave differently when being observed. Spooky action at a distance.
Let's all pretend the last 80+ years of science didn't happen and we live under Newton's ideas of how everything behaved. Who's in?
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
Hey guys, Einstein just called me using GravePhone(tm) and he had the following to say:
"Okay, maybe God does play dice, but I still stand by the law of conservation. God doesn't just make shit up. Now if you'll excuse me, Aristotle wants some one on one on the basketball court."
#fuckbeta #iamslashdot #dicemustdie
Special Relativity makes quite clear that if two particles are spacelike separated when measured, that the concept of "instantaneous" is devoid of meaning.
If you have this kind of distance than you will have just one special reference frame where this is true, and infinite more where the events are arbitrarily separated in time. This is already at the core of the EPR paradox.
I.e. that you can have entanglement across time follows trivially from SR and the EPR paradox.
It's just astounding how many times the very same insight can get repackaged and sold as new.
We already knew that.
Whatever "we" you mean count me out.
According to GR gravity is facilitated via a retarded potential, and of course GR survived so far every conceivable test and has been shown to make correct predictions were Newtonian gravity failed.
So no, gravity does not operate faster than light.
When you read the article, this isn't actually too controversial. All that's being done is changing the timing of of when the measurements are taken and when the intermediate photons become entangled. It's really just using the entanglement process to spread out the time over which the quantum state data is transmitted. You basically have a quantum data historical record.
I can certainly see this opening up useful new capabilities in quantum computing and measurement of quantum phenomena, but it doesn't change our understanding of quantum events and how they interact with our "everyday notions of space and time.".
Yeah, this. What the AC may be confused about is that faster than light travel is (as far as we know) not possible in space, but the distance between two points can increase faster than light could travel because there's nothing stopping space itself from expanding that fast.
sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});
According to the article, particles 1 and 4 do not coexist. Therefore, one must be destroyed before the other is created.
But if 1 is destroyed before 4 is created, then the entanglement of 1 and 2 is broken before 3 and 4 are created (because 3 and 4 are created together, and then 2 and 3 are entangled).
So, by the time 2 and 3 are entangled, 1 does not exist, because 3 already exists and is entangled with 4.
The question that arises is then how do they know that 1 and 4 are entangled?
It could simply be that 1 and 4 show the same state when measured, because 1 and 2 were entangled, then 3 and 4, then 2 and 3. Which means that whatever entanglement existed between 1 and 2 will exist between 1 and 3 and 1 and 4, even if 1 does not exist.
That does not mean particles are entangled across time. It may mean that entaglement is simply peristent and transmiitable.
Most probably there is a misunderstanding somewhere between the announcement and the article, so please anyone that knows more, elaborate.
Entanglement can be used to exchange keys for secret communication. It allows two parties to create a shared key without anyone being able to intercept it. In principle, this key can be as long as the message itself and perfectly random, so a simple 'xor' operation is all it takes to make the message completely undecryptable. In more detail:
Alice wants to send a secret message to Bob.
They (or anybody else, really) create a bunch of entangled photons, half going to Alice and the entangled counterparts going to Bob. This all happens at normal speeds (not faster than light), but can be prepared in advance.
If anyone tries to eavesdrop during transmission of the entangled photons, Alice and Bob are able to detect the fact that the photons are no longer in a superimposed state and start over with a new bunch.
Now Alice and Bob measure the photons. They have no control over the outcome of the measurements, which will be completely random, but they do know that they will both get the same result (or rather, exactly the opposite result). This becomes their cryptographic key.
Now Alice encrypts her message with this key and sends it to Bob using traditional communication channels, for example a carrier pidgeon.
Bob uses his identical key to decrypt the message.
The only faster-than-light part of the story is that the entangled photons "chose" their state at the time of the measurement. Before the measurement, they were in a superimposed state. This means the information for the key didn't even exist yet in any way and can therefore never be intercepted by anyone. It only came into existence at the time the photons were measured, simultaneously for Alice and Bob. (Take the word "simultaneously" with a grain of salt, because as the article shows, they can even be separated in time). And the encrypted message without the key is just a series of random bits.
The problem is that to be accepted in an area of science that's basically nothing more than a consequence of the maths, you have to show the maths that generate the results you expect.
I'm a mathematician. I don't claim to understand 1% of 1% of quantum mechanics at all. But it comes from a mathematical model that happens to have real-world consequences that are weird and wonderful. When we then tested for those consequences, we found out that they exist in nature. Which, to a scientist mind, kind of hints that the maths must have been at least somewhat correct (or at least on the right lines).
I have my own understanding and theories, but I would also have to state, quite clearly, that quantum physics isn't really "physics". This isn't Newton seeing an apple fall and realising there's a force at play. This is someone (probably THE most famous genius) sitting down for decades with almost unsolvable equations that make absolutely no sense until they realise that it works if you have 11 dimensions, or if space and time are two different elements of the same thing, etc. And that was back in the 1900's when quite a lot of physics and maths we enjoy now didn't even exist.
Then you go out and measure in real life and you find that, actually, it turns out that your theory fits what happens in the world, not the other way around.
As such, I don't for a second think that I can just posit a hypothesis (theory is a slightly stronger word in any science) and have any concept of if I'm talking gibberish or not. The maths of quantum mechanics is horrendous and complicated and quantum theorists spend more time in front of the blackboard than they do the LHC.
If you wish to contribute, even if you don't intend to be taken seriously, it's only proper to get yourself a decent grounding in not just "hey, there's something smaller than an electron and weird stuff starts to happen at that scale, I bet I can guess what else happens", but in WHY that's so and HOW we got to that point. And in anything quantum, that means understanding the maths behind it.
As someone with a degree in maths, I tell you now, you're going to need a decent grounding in quite a lot of basic physics and huge amounts of maths and that "real world intuition" will basically be next-to-useless until the very end. That's not to mention the level of things like calculus and linear algebra you'd need to even get close to learning how we got to all of the old "wrong" models, let alone the newer ones.
This doesn't mean that wild ideas and theories have no merit, it's just that you're theorising about something that you probably don't understand the basics of. I know I don't. And I *can* read the mathematics and, given enough time, understand it.
It just comes across to any mathematician or physicist as someone who is looking at a car for the first time and saying "You know, I bet if you made the whole thing ten times bigger, it would go even faster" or "If it goes that fast with four wheels, imagine what it'll do with 10!".
In a way it reminds me of the Moon conspiracy theorists. They can come up with a million weird and wonderful things that intuition says "must be wrong". But it turns out that a few simple tests or bits of maths show them to all be nonsense. "The shadows are wrong" - fine, go out into the street on a sunny day and try hard to replicate them. If someone can replicate something that's "wrong" in the space of ten minutes, then maybe you are reading far too much into the image, or commenting on something you just don't understand.
https://en.wikipedia.org/wiki/Introduction_to_quantum_mechanics
Seriously, just on that page there are some 16 equations, and that's not even a millionth of what you need to understand where those equations come from.
Honestly, I DON'T understand quantum mechanics at all. I believe it, because it's accepted as the best self-consistent theory we have that has made verif
Space itself can expand at much greater velocities than c.
To explain this in a little more depth, what we call "space" is really just tied to an arbitrary choice of space-time coordinates. If we choose a different reference frame, distances and times will be different. Just to give a silly example, if I define a meter to be the width of an atom, or if I define a second to be the time required for the earth to go around the sun a thousand times, I can easily travel faster than c. So how does this apply to cosmology and general relativity?
Depending on the coordinate system you choose, the universe can really look radically different, even to the point of no longer being infinite. I will give two possible views, both equally valid even thought the first may appear strange. (So read the rest as well before labeling it as rubbish).
You can apply a classic "special(ly?) relativistic" coordinate system to the universe, with us at the center. The speed of light is the same everywhere, relative to us, just like Einstein said in the beginning. Things that are far away from us are moving away at high speed (but less than the speed of light) and are therefore aging more slowly. This means that some far away galaxy isn't just younger (defined as the amount of local evolution after the big bang) because we had to wait for its light to get to our telescope, it actually is younger "right now" even if we take the traveling time of light into account. Local clocks are really advancing more slowly. The effect increases with increasing distance, and at a distance of c times the age of the universe, the big bang is happening as we speak. Right now. This also means that the universe is finite (assuming nothing existed before the big bang, which is a big assumption). Not that it matters much, because we could never reach this "edge" anyway. It is retreating at the speed of light.
This model is quite interesting but a bit cumbersome for cosmology, so most people prefer to use the "cosmological model". They simply adjust the coordinates of time and space so that the whole universe is the same age and looks roughly the same everywhere, "right now". See, we just changed the definition of "now" and chose a coherently matching set of space coordinates so everything looks rougly the same size, that's all we did. In General Relativity, we are completely free to do so, you can pick pretty much any coordinate system you like. Things can move from the future into the past and back again as we change our variables, without impacting causality (which is all that matters).
Using the cosmological model, the universe is now truly infinite, the big bang is in the distant past everywhere and all the clocks are running at the same speed (as long as they are stationary relative to "space", i.e. moving away from us at the same speed as the average local galaxy). Now, however, the assumptions of special relativity no longer hold. In particular, the speed of light is no longer the same everywhere. Light speed is still the same everywhere locally, relative to "space" (the speed of the average galaxy in that area), but you have to take the properties of our peculiar coordinate system ("expanding space") into account. If at some distance, "space" and the objects in it are expanding away from us faster than the speed of light, the light from those galaxies will never reach us since it will actually be retreating as if it were running towards us on a conveyor belt moving the other way at a higher speed. The conveyor belt isn't "real", it's just an artifact of our choice of coordinates which does not comply with special relativity.
In the first model, those distant galaxies simply never come into existence since the local "space" is asymptotically stuck at a time shortly after the big bang. Things over there are moving away from us at increasing velocity approaching c, and time (rate of aging of that part of the universe) is grinding to a halt.
But do those places exist or not?