Theory of Relativity

[mal4mac]

I think the balloon concept is a way to explain how space expands. So on top of the motion away from us of the furthest galaxies, space is also creating distances between us and these galaxies like the stretching surface of a balloon or, to use a different image, the surface of a loaf of bread that is rising in the oven. The dark energy is like the yeast in the bread that makes it rise.

I think you're slightly mis-using the bread metaphor. It's usually used to bring three dimensionality into the situation. The surface of the bread takes us no further than the balloon.

Imagine galaxies as raisins in the bread - you can (just about) visualise the raisins all becoming further from each other as the bread expands - like the ink spots in the surface of the balloon but now we have 3D. I like yeast being used as the metaphor for dark energy though...

For the seven year old I'd start with the balloon metaphor, though, and sympathise with any difficulty in visualising the bread metaphor. Maybe actually bake the bread and measure distances between raisins! In "Universe in a Nutshell" Hawking admits that he can't visualise *every* situation fully in 3D - only in 2 dimensions, or, at a stretch, 21/2 dimensions... made me feel at a lot happier about my limitations in visualising things...

P.S. as space actually is "flat", according to the most accepted standard model, the bread model is a precise model of the expanding universe. A bright 7 year old might complain about using the balloon model, as the universe obviously isn't 2D! Like using a cardboard cut out instead of a 3D action man - just wrong. The bread model gets round that...

[YesNo]

The Dog School of Mathematics: Special Relativity

Actually, my link was to Chapter 2. You should start with Chapter One.

The page on focal-plane shutter cameras from this series was interesting: http://conduit9sr.tripod.com/SR12.html

In the link is a photo of a car at a race where the type of camera used, the fact that the photographer moved the camera and the speed of the car created a distorted image. The goal was to use the picture to show how relativity made a person looking at an object in motion would see time dilation or shorter lengths than expected.

This does involve light and motion and, like the balloon or raisin bread ideas that mal4mac and I have been using, may have something that can mislead as well as illustrate.

The car's speed however is not even close to the speed of light although the distortion of the wheel is obvious.

There's also a problem with "beginning" of the universe. Things begin in time. How can time begin in time? The universe just begins, it doesn't begin in time, because time is created at the moment of the Big Bang. (Rats, I used "begin" again... and "moment"... how do we get away from time-dependent terms so we can talk about a time without time (!)?)

I suspect, because it happened once, the Big Bang happened many times. Our space-time starts when matter is transformed from energy to become a universe, but that doesn't mean it is the only universe that exists. These other universes need not be connected nor overlap since they create their own space-time upon expansion. It may not be possible to get experimental evidence from within one to detect the other.

The problem with the beginning of our particular universe is that it requires a cause of some sort. That cause either involves a conscious choice or not making the cause a justification of either theism or atheism. Whether the cause is conscious or not, it is hard to make sense of a cause that triggers a space-time to start. Usually a cause has a temporal component to it.

I also finished a quick reading of Aczel's Entanglement which is an historical survey of the confirmation that quantum theory implies non-local behavior.

Entanglement is when two quantum objects are created in such a way that when the spin is detected as either "up" or "down" in one, the opposite spin is determined in the other. Prior to detection, the spin is random. It could be either up or down. This spin determination occurs across large distances that light could not travel in time to let the entangled object know that the spin of its partner had been detected and so its spin is now determined.

Although it is not information or mass transmission, this determination happens instantaneously. I don't think there is any speed associated with it at all. That is, it happens faster than the speed of light.

Einstein, Podolsky and Rosen challenged physicists to either accept non-local behavior or acknowledge that quantum theory was incomplete in 1935. John Bell re-formulated the challenge between 1964 and 1966 so that it could be experimentally tested. The non-local behavior of quantum theory was confirmed later in the last century.

Just something more to try to tell the 7-year old.

[mal4mac]

I suspect, because it happened once, the Big Bang happened many times. Our space-time starts when matter is transformed from energy to become a universe, but that doesn't mean it is the only universe that exists.

The standard model assumes that space-time and energy start at the moment of the Big Bang. I can't see what "energy *then* matter and s-t" gives you! Not even sure it' s thinkable - if it's kinetic energy then motion happens in time... I can't see how you can get away from time being the first thing to appear... maybe along with other things...

These other universes need not be connected nor overlap since they create their own space-time upon expansion. It may not be possible to get experimental evidence from within one to detect the other.

That looks like standard M theory, where M can stand for Membrane, each universe on a different membrane. Brian Greene is quite good on that theory. Last I heard they were looking for distortions in the MWBR that might indicate a brane collision.

The problem with the beginning of our particular universe is that it requires a cause of some sort.

Does it? Why?

Entanglement is when two quantum objects are created in such a way that when the spin is detected as either "up" or "down"...

I think the key points are (i) that the particle system acts like one object, (ii) everything in the system acts at the same time. So why not, instead of all these boring spin particles, talk about an "entangled toy robot". If you turn on the switch on its back, it says "Hello, Jack Robinson. Danger! Danger!" (or whatever). Take the switch off its back and place it on the moon, mars, Andromeda galaxy, wherever, turn it on and in that instant the robot still comes alive just as if the switch was on its back! But you can only get pictures of the Robot responding much later, due to the limit of the speed of light, hence information cannot travel faster than light, but you can get an entangled system that acts as one thing, and makes it seem like faster than light 'something' is going on. But as entangled objects act in the same "now" I don't think it helps much to talk about faster than light anything going between them... anything going between objects requires time to go between them doesn't it? Also, we haven't spotted any strange radiation going between objects in "now" time...

I think going on about Bell's proof should be left until he's 22

[YesNo]

The standard model assumes that space-time and energy start at the moment of the Big Bang. I can't see what "energy *then* matter and s-t" gives you! Not even sure it' s thinkable - if it's kinetic energy then motion happens in time... I can't see how you can get away from time being the first thing to appear... maybe along with other things...

Kinetic energy would be within space-time. From within any particular space-time universe, the Big Bang was when energy-matter was created. Because energy moving at the speed of light has only a hear-now space-time makes me think that this energy may have a reality separate from any space-time.

I guess I don't like seeing things being created out of nothing.

That looks like standard M theory, where M can stand for Membrane, each universe on a different membrane. Brian Greene is quite good on that theory. Last I heard they were looking for distortions in the MWBR that might indicate a brane collision.

In that case the brane collision would link the two universes together if that actually happened. However, in general I don't see why two separate space-times each with their own Big Bang should ever have contact with each other. They create their own space-times. They don't consume the space-time of a separate universe and so should never have occasion to collide with another one.

I think the key points are (i) that the particle system acts like one object, (ii) everything in the system acts at the same time. So why not, instead of all these boring spin particles, talk about an "entangled toy robot". If you turn on the switch on its back, it says "Hello, Jack Robinson. Danger! Danger!" (or whatever). Take the switch off its back and place it on the moon, mars, Andromeda galaxy, wherever, turn it on and in that instant the robot still comes alive just as if the switch was on its back! But you can only get pictures of the Robot responding much later, due to the limit of the speed of light, hence information cannot travel faster than light, but you can get an entangled system that acts as one thing, and makes it seem like faster than light 'something' is going on. But as entangled objects act in the same "now" I don't think it helps much to talk about faster than light anything going between them... anything going between objects requires time to go between them doesn't it? Also, we haven't spotted any strange radiation going between objects in "now" time...

Putting the switch on the moon would require some time before the robot realized it was turned on. However, what you mention about happening in the same here-now does seem to explain how entangled photons could influence each other across great distances. From their perspective, it is no distance at all.

[mal4mac]

Putting the switch on the moon would require some time before the robot realized it was turned on. However, what you mention about happening in the same here-now does seem to explain how entangled photons could influence each other across great distances. From their perspective, it is no distance at all.

It would take some time to take the switch to the moon, by some Russian space craft maybe, but once there the switch would act just as if it was on the robot's back - we are assuming the switch and the robot are "entangled", of course, so we would have to create an entirely new technology. Do you think the Dragons would give us £100K to R&D this?

[YesNo]

It we assume things that large could get quantum entangled, then flipping the switch on the moon should instantaneously make the robot move.

However, that does seem like information transfer faster than the speed of light. Now I'm aware that the non-local quantum behavior is supposed to avoid any violation of special relativity, but I am beginning to wonder why that is claimed to be the case. Suppose the state of one entangled photon is observed, the state of the other is now determined, but how does that other photon know that it's state has been determined? That looks like information transfer faster than the speed of light.

[mal4mac]

It we assume things that large could get quantum entangled, then flipping the switch on the moon should instantaneously make the robot move.

However, that does seem like information transfer faster than the speed of light. Now I'm aware that the non-local quantum behavior is supposed to avoid any violation of special relativity, but I am beginning to wonder why that is claimed to be the case. Suppose the state of one entangled photon [A] is observed, the state of the other is now determined, but how does that other photon [B] know that it's state has been determined? That looks like information transfer faster than the speed of light.

Observer of A (OA) assumes that the state of B is determined, that is, OA knows, if his theory is correct, that because A is "down", B must be "up". But he can only know this *for sure* by getting a message from OB, and that message has to travel at light speed.

Therefore information, which must be actual experimental verification, is limited by the speed of light.

If OB measures B as "up" he has no idea if A is "down", or anything about A, until OA tells him, and that "telling" is also limited by the speed of light.

[YesNo]

I agree. From the observers' perspective they cannot communicate faster than the speed of light using entangled particles. I guess that is the "no-communication theorem": http://en.wikipedia.org/wiki/No-communication_theorem

However, if the particles are entangled, there is something known about a distant location that happened instantaneously. Suppose two particles have been entangled and are now a light-day away from each other. Bob measures one of the particles to have the "up" property. Immediately, Bob knows that Alice's particle is "down" whether she has already measured it or not. This is not because Bob's particle was always "up". It was not "up" until the first measurement occurred which Alice might have already made. It could just as easily have been measured "down". It is true that Bob and Alice would have to wait a day to get confirmation of the non-locality result, but if the non-locality theory has been established, they would just invoke it and not bother asking the other what their measurement was. They would already know.

Because of the time component, it makes one wonder, as Cioran mentioned in a separate thread, in whose frame of reference do we say that Bob made the measurement first or Alice made the measurement first? That would be the relativity question for this thread.

In any case, this is one way for Bob and Alice to individually flip a coin and get information on the results faster than the speed of light. They don't know what the results will be until they perform the flip, but once one of them does, the coin flip has been determined for both across potentially vast distances of space.

[cacian]

I think I would see it this way.
The universe is the origin to a simple question:
''Where do we begin?'' and not ''how did we begin?''
Only for the simple reasons that my probabilities of finding the answer to the first question is more likely to lead me to many possibilities.
Eventuality is a fact of life. Durability is not so because each individual life span is relative and that is enough.
And so the second question is less pressing because it contains many insolvencies and takes me nowhere.

A similar example to clarify the above post is bit like this:
I look at bird and I wonder:
'Where does it fly to' and not 'how does it fly'.The where is the origin.
The how is pointless.

[YesNo]

"How" does seem to dwell on the past. "Where" seems open to the future.