heh. Thanks
Thanks for the great thread and info here. This point always hurts me head, however.
I understand that looking out 14 billion light years, we’re seeing light that is 14 billion years old. Quasars and all that jazz, stuff from the “birth” of the universe.
But doesn’t that also mean that the stuff we’re seeing was also 14 billion light years away from us at the time it sent the light our way? Which means that our universe was at least 14 billion light years in radius 14 billion years ago, and there were lots of things out there then.
Sorry if this point is confusing, I guess I’m just trying to wrap my head around it. It seems to me almost like geology, like layers in a rock-- look 14 billions years away, then look 10 billion years away, etc., until you start getting closer to us you see objects that “evolved” into galaxies, stars, etc.
If that’s true, then conceivably the quasars we’re looking at out on the edge of the universe are now not only further than 14 billion light years away (and thus unable to be seen), but have evolved into other stellar structures and forms, etc., that we will never get to see.
Right?
I’ve heard this before, so I’m not arguing. But I do not understand it, and I hope someone can explain it to me.
I think this would work best if I demonstrate that I already understand about shadows, and then maybe someone can explain about quantum entanglement.
Suppose I shine a flashlight into the sky, so that it can be seen by someone on a planet of a distant star. Also suppose that my flashlight is incredibly bright, and that the sky is incredibly dark. When I put my hand in front of the light, it will cast a shadow upon that planet. (It will take many years for the light and shadow to arrive there, but I don’t think that is relevant.) If I move my hand, the shadow will move. Even if I move that hand very slowly, the shadow will pass accross the surface of that planet almost instantaneously. In fact, the shadow will move at many times the speed of light. (See footnote for calculations)
But there’s no way this shadow can carry any information from one side of the planet to the other, because the shadow does not originate anywhere on that planet. It is a result of the motion of my hand, all the way over here. If any information is going to move, it will be from Earth to that planet, and at a speed no faster than the speed at which the shadow itself travels from Earth to that planet – which is the speed of light.
But if my understanding of quantum entanglement is correct (which it apparently isn’t, so please correct me), then I can have a particle here, and a corresponding particle on that distant planet, and I can do things to this one, which will have instantaneous effects over there. Why isn’t this a transfer of information? I admit that it will take a long time to set up, but can’t I have a whole bunch of these particles, such that one of each pair is here, and the other is over there, and I can send a message by manipulating some of them but not others? Keep the particles in sequence, and we can use Morse code, or ASCII characters, and have a genuine telegraph. Why not?
Footnote: Suppose my hand is 10 centimeters from the light, and I move it at the incredibly slow speed of one millimeter per second. The nearest star (Alpha Centauri) is about 41,000,000,000,000 km away, and the shadow will move across it at about 410,000,000,000 km/sec. The speed of light is only 300,000 km/sec.
Because even if you take an interpretation that you have affected those particles on Alpha Centauri (which is not a given in all interpretations of quantum mechanics), there’s no way the Centaurans can tell that you’ve affected them until they receive a classical communication telling them that you did so.
What entanglement produces is **correlation **of results.
Say you’re measuring the spin of the particle. It has a 50/50 chance of being up or down. So if you measure ten particles in order you’ll get a sequence like:
UDUUUDDUDD
As far as you can tell it’s a completely random sequence.
Meanwhile your friends on the distant planet measure their particles. They get:
DUDDDUUDUU
As far as they can tell it’s also a completely random sequence. The only way to tell that they’re not random is to actually compare the two. Then you realize that every time you measure “up” the other planet measured “down” and vice versa.
This is starting to make sense. Thanks very much.
Is this possible? Set a hundred of them all the same way. The hundred on the other end will also end up the same way. This is a signal that a message is coming, with no need for comparing. Then send the message, again with no need for comparing.
I know it won’t work. But why?
Because it only works if they’re in a unknown state. If you interact with them to put them in a particular state you break the entanglement.
Oh!
Well, I guess that’s that. Thanks!