This Universe may be made up of eleven dimensions but seven of those are at the quantum level so cannot be experienced
A one dimensional Universe is theoretically possible but since light cannot pass from one to another then there is no way of verifying that. However some multiverse theories incorporate universes within universes but they are not accessible to light either and so the point is still academic if somewhat intriguing

surreptitious57 wrote:This Universe may be made up of eleven dimensions but seven of those are at the quantum level so cannot be experienced

Really? When are you due to fly to Stockholm?

hackenslash wrote:
You do it when you're standing still.

Are you sure? I thought we were always in some sort of motion.

Animavore wrote:Are you sure? I thought we were always in some sort of motion.

Strictly, everything in the universe has equal claim to being at rest. There are caveats, such as that you can't strictly claim to being at rest in a gravitational field (i.e. it's not an inertial frame), but essentially the core idea is that you're travelling through spacetime at a fixed rate, regardless of how much of your travel is taken up in which dimensions. When you stand still in space, all your motion is through the time dimension, and when you travel through space at light speed, you don't travel through time.

hackenslash wrote:

Animavore wrote:Are you sure? I thought we were always in some sort of motion.

Strictly, everything in the universe has equal claim to being at rest. There are caveats, such as that you can't strictly claim to being at rest in a gravitational field (i.e. it's not an inertial frame), but essentially the core idea is that you're travelling through spacetime at a fixed rate, regardless of how much of your travel is taken up in which dimensions. When you stand still in space, all your motion is through the time dimension, and when you travel through space at light speed, you don't travel through time.

Oh yes. You're correct. It's like the Bart and Lisa thing from one of Brian Greene's books where if you're just floating there deep in space and someone seems to fly right past you to them you are the one flying past and there's no way to tell the difference.

Animavore wrote:

hackenslash wrote:

Animavore wrote:Are you sure? I thought we were always in some sort of motion.

Strictly, everything in the universe has equal claim to being at rest. There are caveats, such as that you can't strictly claim to being at rest in a gravitational field (i.e. it's not an inertial frame), but essentially the core idea is that you're travelling through spacetime at a fixed rate, regardless of how much of your travel is taken up in which dimensions. When you stand still in space, all your motion is through the time dimension, and when you travel through space at light speed, you don't travel through time.

Oh yes. You're correct. It's like the Bart and Lisa thing from one of Brian Greene's books where if you're just floating there deep in space and someone seems to fly right past you to them you are the one flying past and there's no way to tell the difference.

Yep. Fabric of the Cosmos, another of my top recommendations.

The entirety of the principle of relativity is that you can't tell from experiment that you're moving as long as your velocity remains constant.

I have the book and have also read it but cannot recall it all from memory but it was very accessible
And hell of a lot easier to read than The Road To Reality which was akin to trawling through treacle
I really should not have bought it knowing in advance it was going to be virtually impossible to read
But knowledge picks up gradually if one is interested in any subject matter so it does not bother me
I intend to re read Why E Equals Mc Squared again any way just to re fresh my memory and keep up

surreptitious57 wrote:Mc Squared

Is that fast maths?

What happens to the speed of a photon outside of a vacuum ? Does it
slow down or does it keep travelling at c ? And if it keeps travelling at
c then why does the vacuum have to be referenced in the first place ?

Evolving wrote:

surreptitious57 wrote:Mc Squared

Is that fast maths?

Isn't it the new breakfast burger?

surreptitious57 wrote:What happens to the speed of a photon outside of a vacuum ? Does it
slow down or does it keep travelling at c ? And if it keeps travelling at
c then why does the vacuum have to be referenced in the first place ?

We've had this discussion before, surr.

In normal physics, we say that light travels more slowly through a medium, and this is why it is refracted when it hits a prism at a slant to its surface, or any boundary between two differently transparent media. That is why we are always careful to add that c is the speed of light in a vacuum. One can see this very beautifully by considering light as a wave and considering the wave equations that describe its propagation (N.B these are not the quantum wave functions that Schrödinger and Heisenberg worked on, but the normal classical waves that Maxwell dealt with).

If we are looking at light as particles travelling through a medium that also consists of particles that are separated by vacuum, then it is a different matter, and here the photons are indeed propagating at c while they are bridging those vacuous gaps, and the rest of the time they are absorbed and re-emitted by the particles constituting the medium in a way that exactly corresponds to the way Maxwell's waves behave. Twistor dealt with this aspect in the last thread that addressed this question.

Thanks for that Evo. I will take notes and commit to memory
I did not know that it had been answered before so apologies
for asking again. So hopefully this time I shall remember that

I've been looking for the previous thread, and have just surfaced to check this one. Back when I've found it!

[holds nose and sinks]

glug glug

We discussed it HERE, among other places.

Yeah, I was thinking of a different, earlier thread, in which I answered along much the same lines as above and referred to a still earlier thread that I vaguely remembered in which Twistor had posted a link; twistor himself then swooped in and didn't remember that earlier thread, but posted a link anyway, saying more or less what I reported in the last part of my reply above; but I'm buggered if I can find it now.

Dunno, but I've seen this come up in several threads, and I know one of the links twist posted will have been this one from Physics Forums.

Good link; don't think it's the one I remember, but it is illuminating, and incidentally totally debunks what I wrote in my last paragraph in my reply to surr and exposes it for the bollocks that it was.

Ah well. I'm reasonably comfortable with classical electromagnetism, but have a good way to go on the quantum side.

Evolving wrote:Good link; don't think it's the one I remember, but it is illuminating, and incidentally totally debunks what I wrote in my last paragraph in my reply to surr and exposes it for the bollocks that it was.

Ah well. I'm reasonably comfortable with classical electromagnetism, but have a good way to go on the quantum side.

Haha, I was just reading the thread and having a laugh at the goings on! I think I found the link you were looking for Ev:

http://www.rationalskepticism.org/physics/idiot-s-guide-to-relativity-t516-60.html#p1844862

It doesn't throw that much errrrr light on the subject!

OMG futher down the thread, I called Dave Mc Culloch a dipshit. That's really appalling behaviour on my part - calling Dave Mc Culloch a dipshit I mean. I would like to be clear that I do NOT condone the assignment of the term "dipshit" to Dave McCulloch.

Yes, that was a fun thread.

Bingo, twistor, that is exactly the thread I was remembering. Buried in a completely unrelated discussion about relativity. Small wonder that I couldn't find it.