Please explain to me quantum entanglement.. and can we “ hypothetically “ build a quantum entangled cameras or some sort of optical device one we can observe on and them put this device in a space shuttle or smt then we can observe events in time ?
Let’s just say this device is 1 light years away but it’s entangled with a device here on earth so events will reach us 1 in 1 year or just in time?
In: Physics
This is hard to ELI5 because some of these concepts don’t have an ELIPhD yet. Quantum Entanglement is a topic at the fringe of human knowledge. The most well-trained people in Physics are still trying to answer these questions. If they don’t know the answer, there’s not an ELI5.
We know what it *is* enough.
Quantum Physics deals with special particles that are even smaller than the parts of an atom. Just like atomic particles do weird things, these do weird things. So weird we argue they have their own special Physics.
Dealing with these particles is hard. We can’t see them. Even with a microscope. To visualize what we have to do, imagine a silly experiment. You’re in a room with no windows. To your east is a room you know has some balloons floating inside it. There is a cannon that will shoot a foam ball on the wall. You can get it to shoot the ball at any angle and velocity, thus you can make the ball hit any part of the other room.
This is actually enough to figure out where the balloons are! You can fire a ball at an angle, and if you don’t hear it hit a balloon, you know there are no balloons along that path. With the right tools, you can start forming a 3D image of the room and show where balloons aren’t, and it will get more and more likely you find where a balloon is. But, alas, if your ball hits the balloon, it’s going to get moved somewhere else. So you can only really figure out where a balloon *isn’t* and where a balloon *was*, though after you hit a balloon you can make some guesses where it may have went.
This is what it means to “observe” quantum particles. They’re so tiny that photons of light actually have an effect on them. So we “see” them by firing particles at where we know one is, and we observe how the particles reflect back, kind of like listening for a ball hitting the balloon. How the particles reflect back tell us about where the particle was and what it was doing. But it only works the one time. This is what’s meant by saying “observing” the particle changes it. It’s technically always changing, but in one specific moment we do a specific thing to find out what it was doing at that moment.
For “entanglement”, things get weird. We have figured out that, for reasons, two quantum particles can be “entangled”. That means whatever one is doing, the other is also doing. We still don’t fully understand this, but we understand it enough to figure out if it’s happening and to cause it to happen to some particles. What is really “weird” about entanglement is so far as far as we can tell, if you change one particle the other changes “instantaneously”.
Now, “instantaneously” is a crazy word in Physics. Normally when something happens in Physics, it happens “fast”. Like, if one object collides with another, it *seems* instantaneous that they react but in reality force is being transferred in nanoseconds and other tiny intervals.
This is, as far as we can tell, *instantaneous*. Zero time passes. And, more mysteriously, having more distance between entangled particles does NOT so far produce a measurable delay. That’s stupid exciting.
It leads us to think things like:
> can we “ hypothetically “ build a quantum entangled cameras or some sort of optical device
“Hypothetically” yes! If we could somehow make an image sensor consist solely of entangled particles, we could maybe find a way to use the particles where we are to form an image over *infinite* distances instantaneously. That’s still really hard! Remember, to observe particles we have to change them. And entanglement works 2-ways. And so far we’re very limited in how we can purposefully cause entanglement, or how far apart the particles can be, etc.
The problem is there are different degrees of “hypothetical” depending on how much we’d have to figure out to do it. For example, “useful nuclear fusion” is a small “hypothetical”. If we funded it with as much money as we spend on cryptocurrency, Physicists are pretty sure we could have it within 20 years. It’s just right now we’re choosing to spend an amount of money on it that leads the Physicists to estimate “never”.
If we call the distance from us to nuclear fusion like “500,000 miles”, the distance from us to some form of quantum camera is something like the distance from us to the next galaxy. We can’t comprehend how to get there. There’s too much to figure out. We’re not even sure if we CAN figure it out. But the possibilities are so exciting we’re willing to let people spend their entire lives trying to figure it out. Any breakthrough we make could cut that distance back down to something reachable. It’s just it’s hard to tell what you need to know when you don’t know what you don’t know.
The most simple explanation of quantum entanglement is just an extension of the idea that mulitple objects cannot exist in the same place at the same time.
It turns out, for very small objects, “place” is not the only detail about objects that obey that rule. There are other things like electric charge, momentum, etc… That cannot be the same at the same time.
At that scale, we do know that there are minimum measurements for these things, though, and we can see that the total system might have a certain value.
And because these tiny objects don’t have location in the same way that much larger objects do (they’re excitations in fields. Or they’re wave functions that collapse. Or *maybe* they’re vibrating strings. But they’re *definitely not* points in a specific place), they can interfere with each other in this way over much larger distances than would be possible, otherwise.
But for basically the same reason, in order to verify that they’ve actually done so, you have to independently observe all of the entangled particles and measure their individual traits before you can know for a fact that they interfered with each other.
You get entangled particles typically when they are created in one event. The most basic example is spin, you have a particle with 0 spin and it decays into two particles with both spin 1. Now you know that whatever direction you look one particle must be spin +1 (up) and the other has to be -1 (down) because angular momentum is conserved.
We know that there are no local hidden variables which would be equivalent to the particles picking down or up at the moment of their creation, for a given axis they are in a superposition lets say 50% up + 50% down, but angular momentum is conserved. How do we know that they didn’t pick in advance? If you were to measure one particle along a different axis you wouldn’t get 50-50 +/- 1 in that direction you’d get some slight skew towards one which is not what QM tells us and experimentally the prediction that QM makes is the valid one.
So we can say that when I measure particle A it goes into the spin up state and immediately particle B enters the spin down state regardless of their distance. This may at first give the wrong impression that you can send information faster than light (FTL) through this process but no you can’t. For one you didn’t get any information FTL because all information was available locally to figure out the spin of particle B. You know they were created from one event and so you know they have to be entangled to make sure angular momentum is conserved and you measured the spin of particle A. The whole system (this two particle system) contains these two pieces of information. You also didn’t send information because a quantum system doesn’t hold information about its “measurement status”, meaning you cannot preform any experience on B to show that its “wavefunction has already collapsed”.
From my limited understanding in an ELI5 way entanglement is particles that have mutually exclusive but related states.
Classic analogy is like a pair of gloves (or shoes). The pair is related in that there’s always a right and a left one.
if you split up the pair into 2 boxes you know one box has a left glove the other a right. If you open up one box you know what the other contains.
the second half of the “spooky action” is the superposition that their state in the boxes is undetermined and “collapses” to a known state. “Hidden variables” or the idea that one box definitely always has a left and one box definitely always has a right has been disproved through some fancy statistical analysis.
So the reality is more, you close your eyes, split up the gloves into boxes then suddenly both boxes contain one glove that is simultaneously a left and a right glove at the same time. The original mutual exclusivity is the same. if you open up one box the other definitely contains the other pair but the glove you get is actually completely undecided until you look and there’s no way to coerce a given box to reveal a given glove so you can’t transmit any data since you can’t manipulate the final state. also you can’t look at the box and “know” that the state has now been set since the only way to know is to look in the box and that would count as well looking and thus determine the state anyway.
long and the short of it is that even though we know something is happening across distances for all intents and purposes it works just like if you split your gloves into boxes randomly and they were always there the whole time and there was never a superposition.
> can we “ hypothetically “ build a quantum entangled cameras or some sort of optical device one we can observe on and them put this device in a space shuttle or smt then we can observe events in time ?
Yes, but it wouldn’t do us any good.
To get an entangled system the parts have to start together. Then they spread out. And the point of entanglement is that when you measure something about one of them, you know what the other must be.
So it would be like getting two boxes, and getting a salt and pepper pot, and putting one pot in each box. Then shuffling the boxes. And then sending one of them up into space.
Sure, when you open the box on Earth you know what is in the box up in space. But that isn’t particularly helpful.
The quantum weirdness with quantum entanglement is that until the boxes are opened up (and the quantum system is interacted with) the system is in a combination of each possible state (so rather than the system being “salt on Earth, pepper in Space” or “salt in Space, pepper on Earth”, the system is in the state “0.7 salt on Earth, pepper in Space + 0.7 pepper on Earth, salt in Space).
Essentially the whole system (of both boxes) is one closed quantum system until they are interacted with, at which point the system opens up into classical one.
But that still doesn’t help us that much; we on Earth know something about what is going on in Space that we didn’t know (and couldn’t know) before, but it is still really telling us something about what happened when we shuffled the boxes in the first place. We cannot use that to get information between the boxes.
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