That's pretty much my favourite physics fact right there. From the point of view of a photon, travel is instantaneous. From the sun, from the next nearest star, from the big bang... It seemed to the photon that it was emitted and absorbed instantaneously.

We also had a brilliant bunch of lectures by Don Kurtz who told us about a book called Mr Tompkins in wonderland, in which the narrative was written by a guy who was a bicyclist in a world where the speed of light, c = 10 metres per second or so. http://en.wikipedia.org/wiki/Mr_Tompkins

We then did a bunch of questions about what that man experienced, what colour traffic lights were, what length his bike and roads were, and what time it said on the clock tower. Just great, that's what makes me want to lecture one day.

there is no indication or evidence that anything exists outside of the universe, or, that there is even such a thing as outside of the universe. The universe is infinite and contains all there is.

well, you could have a multiverse inside our own universe. We can only see so far in the universe. so outside of our viewing could be a completely different universe all together.

if its in our universe,then,its in our universe,,this seems self evident.

Also, all data currently leads to the conclusion the universe is homogeneous.

there is no indication the universe has an edge,,no point in the universe is any older or younger than any other point...

the universe, by definition,,contains all there is.

Definitions are flexible. The universe is currently defined as the totality of existence, in much the same way as the "world" was defined centuries ago.

In theory there could be many parallel universes (where we change the definition to mean " a space time volume with a given set of fundamental physical constants")

There's also the theory that our entire universe is a 2d hologram.

Personally, I don't know why you'd want to limit yourself to anything as prosaic as one existence. The idea that there are infinite universes is fascinating....

Well, that's the problem. There is potentially a huge data set we do not have access to because we cannot see it in anyway. So since there are whole parts of the universe that are physically separated from us, it could be defined as a separate universe, hence multiverse.

It's also possible we live inside a unicorns ass, but there is zero evidence to support that.

There are no parts of the universe that are physically separate from us.

You can't change the definition of things just to fit your hypothesis,,,I could say 2+2=5 ,if I change the definition of 5

Umm... photons have mass.

Why is he saying they don't have mass?

Neutrinos also travel at or faster than the speed of light and have mass.

No they don't. Sort of. It's complicated.

I don't know about neutrinos, but I'm fairly certain they don't travel faster than light. There was an experiment a few years back that seemed to suggest they did, but as far as I know it is now thought to have been an error. It did make for an interesting paradox - I'm told the experiment was only possible due to very accurate GPS, which of course relies very heavily on both general and special relativity. The ftl result undermined their own methodology.

How about -sometimes photons appear to have mass, sometimes they don't.

As for Neutrinos, apparently they also can't exceed the speed of light. The experiment that said they might was flawed.
http://www.gizmag.com/neutrinos-sub-light-speed/22876/

AFAIK, photons have mass, but in a theoretical state of zero velocity they theoretically don't have mass (which can't currently be tested).

As for neutrinos, I said, "at or faster than the speed of light", not "faster than the speed of light". I never claimed they do go faster than the speed of light, because the jury's still out on that one. This is still a debate that divides the physics community and the matter is far from settled.

From what I've been taught, it takes infinite energy to accelerate mass to the speed of light, which would mean neutrinos will never reach the speed of light either, maybe close but not fully, unless maybe all the energy in the universe could be utilized to make it happen, and even then it's questionable.

We don't change the definition to fit the hypothesis, we change definitions as new information or previously unthought of scenarios emerge.

This is the realm of theoretical physics. Some things are very difficult to test, but it doesn't mean we can't hypothesise about them.

By the way, 2+2 can equal 5, for very large values of 2

photons are massless, its invariant mass..you will have to google that,,,,.neutrinos DO NOT travel faster than light.

The universe is the totality of existance and contains all there is..

The universe has no edge ....that would violate every accepted model of the universe...the universe is homogeneous and isotropic..

parts of the universe beyond our vision are not older than our part..we are the same age...

There is ZERO evidence to support any claim of any other universes..NONE..

You can hypothesis we live in a giants ass if you want,,,but there is no evidence to support that...the claim there are other universes,and the claim we exist in a giants ass, have the same amount of evidence..

@robdot how would you respond to this video?

https://www.youtube.com/watch?v=w3TDO1AA1Sw

These theories all seem to be grounded in at least SOME evidence. To say that there is no evidence to support a multiverse seems incorrect. There is no *empirical* evidence, as we can not physically test it, but you can still hypothesize about these things, no?

There is zero evidence the universe has an edge.

There is zero evidence that anything exists outside of the universe..or,,that there is an outside of the universe.
All current data highly suggests the universe Is infinite ,homogeneous, and isotropic .
The data from wmap and cobe satellites ..show the universe is flat Euclidean space...along with the model of an an isotropic and homogeneous universe, highly suggest the universe is infinite.

Claiming that "something" exists,in our universe,beyond our horizon,,,violates some basic beliefs about the current model of the universe. (Homogeneous and isotropic) ,,also,,it's in our universe...

Points of the universe at great distance from us are not older than us...the entire universe is the same age...AND made of the same stuff...

The universe is flat Euclidean space,,,infinite,homogeneous ,isotropic ,and expanding from all points in every direction,relative to the observer.

I'd love to get in on this conversation because this subject really interests me. This video touched on a lot of interesting theories.

@robdot - I don't understand people who think they "know" the answers to the universe. There are unanswered questions in every model. Do you know the answer to what dark matter and energy is? Nobody has yet detected it. Yet, our "universe" is supposedly filled with the stuff.

Let's also define what a universe is. My definition is; it's a place governed by the same set of physical laws.

So we have "our" universe, that we hypothesize about through our observations and measurements. We have theories that say "other" universes exist in some form or another. If their physical laws are different then ours, there would probably be no way to observe them, and therefore no way to prove their existence. Lack of proof is not proof that it doesn't exist.

I could write a book on what i "think" about what our universe is. For simplicity, let me just say that I moved from telecom engineering to software architect. In software, we create programs to run simulations. We create vast game worlds with whatever "physical" attributes we want to program into them. Lets assume we created artificial intelligence. In what context would "it" live? Most everyone assumes it would just be one conscience interacting with us in the form of a robot (Que cheesy Hollywood films).

Let's give it the power of quantum computing. It then decides to understand us (it's creator), it needs to program a simulation that mimics all it knows about our physical world. It wouldn't make one simulation, run it and be done. It would make many simulations, probably simultaneously, tweaking each new one based on the results of the previous ones.

Just imagine where this could lead. This intelligence could figure out how to create a multitude of different, very elegant universes. Its time scale would be different then our time. It's simulation could take seconds on its viewing scale, but appear to be billions of years when observing from within it. We have the power to pause, rewind, replay, tweak our simple creations. Imagine what this super intelligence could do with theirs?

You don't get to make up your own definitions.

A lack of proof ,is exactly that.

If I don't have to provide evidence, I can claim anything. Hence,creationism...God did it.

There is no evidence the universe has an edge or boundary,,in fact,that concept violates everything we know about the universe..
If anyone could actually demonstrate that there is an "outside"to the universe,they would be the most famous person on earth,,and,that would completely destroy every known model of the universe.

You may notice I didn't say we "know" things, I said the data highly suggests,,or,the preponderance of the evidence shows...

we have large amounts of data to show the universe is flat,homogeneous,and isotropic,,,those three observations, HIGHLY ,suggest an infinite universe.
The preponderance of the evidence is ,the universe has no edge. Or boundary,,and contains all there is,,,,that is in fact,the definition of the universe,the totality of existence...

I'm not making up the definition, I'm stating my simplified interpretation of it, which by the way, doesn't counter anything you said.

You seem to think for other "universes" to exist, ours must have some physical boundary at the edge that we can observe. And crossing that would be the only way to get into another universe?

I'm simply saying that a place with a totally different set of physical laws, whether that resides in our universe, or we reside in it, can exist. We aren't able to rule that out.

There is also the possibility that another universe with the same physical laws can exist, but again, impossible to get to or observe.

Let's say I have a computer simulation of a world with no boundaries and AI lives in it. Wouldn't I then be able to duplicate that program, and run it on another disconnected computer? How would these two AI's interact with each other? Know about each other? Even if they are exact copies of each other? Yet inside their world, they have no detectable boundaries.

Let's say they figured out there was another "copy", it wouldn't ruin the physics of their world at all. It would just have to introduce to them the concept that something OUTSIDE their universe exists.

Something that exists in our universe, is in our universe.if it's in our universe, then it's not another universe...
everything else you said is just conjecture.

You don't get to change the definition of the universe just to suit your needs or simplify it...I don't need it simplified..

The Universe is commonly defined as the totality of existence. This includes planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy...

There is ZERO evidence that anything you claim ..exists...there could be other universes,there could also an invisible magic unicorn under my bed,that only I can see...the evidence that either of those things exist..is the same.......ZERO.
Everything else you said about computers makes no sense and doesn't relate to the original subject in any way...

ZERO evidence of dark energy or matter... those are a part of the model you believe to be absolutely correct?

The computers were an analogy. I guess I'm done. I cannot converse with such close minded individuals for very long. If you can't think outside the box, then I have nothing more to add.

Dark energy can be observed and has been measured.
What you mean is you don't want to talk to anyone who refused to accept your baseless assertions.
There was a time we didn't know what gravity was,,that doesn't mean we couldn't see it. Or measure it.

Dark energy hasn't been measured. We don't observe it. We observe effects of something. It is still unknown what it is, or if it really exists.

And don't put words into my mouth.