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Of course it is, by definition. Universe is all of 'it', it is everything. If Universe is not infinite what is that beyond Universe? And if definitions keep changing then we know nothing. The tricky part, at least for me, is not understanding/imagining infinite/whole Universe, but the...

Sounds probable to be true... Phinds, Mordred?

Others more knowledgeable can answer this well. I'd just like to say that if expansion stops all light will eventually reach us (later than sooner I guess) and (future) we might see birth of Universe :-)

Depends I guess. If you are hammering iron to make a sword you transfer quite a lot of energy into unmovable object.

Would you expect it to be in reverse? I wonder though, is spacetime curving/defining just 3 dimensions?

I agree with the point you made, but also, since I am no expert here, while Samshorn seems to know this light speed question very well, how can I put both views together? (so they agree one with another?) see: https://www.physicsforums.com/showthread.php?p=4361004

Not my intention to sound rude, but how do we (really) know anything else outside Earth perspective? From what I saw on another forum, we even don't (really) know if light from Sun to Earth has same speed (and takes same amount of time) as light from Earth to Sun... (We just assume it does.)

Seems sensible, thanks.

OK, let's say we dump the word 'edge', aren't we left with finite object or structure in regard to observable Universe? Klein bottle looks pretty interesting and finite... But again, isn't a circle enough to present the idea that the 'surface' can be considered to be infinite even when the...

A circle too has no edge ('2D ant' walking on it can go on and on eternally) and thus can be considered to be infinite (even though I'd say a circle has finite number of points, each being a Planck length). No matter how we see the circle or a sphere, both are a finite objects, and in this...

If we didn't have all the data as we (luckily) have today (as Krauss says, in distant future spacetime will expand to the point when humans on Earth will be able to observe just our own galaxy and none other, thus thinking that our Milky Way is our whole observable Universe) then (I go on with...

Aren't the exploding stars (supernova) serving us as a cosmic 'candles', for which we know standard universal brightness, and based on the strength/weakness of brightness we receive we can deduce distance to them? And on the cosmic scale there are many supernova every night...

Of course... Though, I was speaking generally.

OK, nothing is being moved or pushed, but the distance between objects does change, so, relatively speaking, the effect to the observer on the one side is same as if the other object moved, right?

I still don't know where I picked that up, but after some searching I got this: Early dark energy from zero-point quantum fluctuations http://arxiv.org/abs/1104.3797 Zero-point quantum fluctuations and dark energy http://arxiv.org/abs/1004.1782 Could dark energy be measured in the...

Hmm, are you saying that expansion of space-time isn't phsically real? I am not sure where I picked that up, I am checking Krauss book 'Universe from nothing', if I find it there I'll post quotes from book, if it's not there I will apologize for 'spouting buzzwords'.

So, is it impossible that expansion of spacetime could somehow act/push on the objects and move them? Isn't the dark energy actually quantum fluctuations having effect on objects when considering cosmic scales?

Yes, a typo, sorry. I meant to say: "Universe (whole of it, not just the observable "part") has to be infinite." Observable Universe is finite though, and with an edge, or else we couldn't meassure its length, right?

(to be deleted)

I see the difference now, thanks for correcting me (I am not English, sorry). I checked the dictionary: RECEDES means "to move back or away", and to my mind, something moving, is travelling... Langauge is not always logical, is it.

The distance between two objects (e.g. stars) can increase without any motion? So, two objects go appart and nothing at all moves? I apologize to ZapperZ, that he had to delete my statement... But I have to ask... On post: https://www.physicsforums.com/showpost.php?p=4354834&postcount=16 I...

Sure, I'll read as much as I manage ;) As for this test/scenario, I'd rather say, we just don't know, until we check ;)

Due to read, thank you!

I didn't even try to compare the two models till now. But in the end, don't you end in the same repetitions of everything to infinity, no matter of the model used? (And I agree, the process is surely different, but the end result isn't. Everything possible happens, in both models.) Let's say I...

If we remove everything from existence we are left with nothing, right? Now, if that nothing is not really nothing, but quantum fluctuations happening everywhere to infinity, then having many worlds or Universes is just "natural" ;) Thanks for the link. (And previous ones too -- all saved for...

It's more probable that whole Universe is infinite than that it isn't. If it isn't then it has an edge. But en edge to what? What can be behind/beyond Universe? Nothing at all maybe? If so, can you define nothing? Is that which is not matter/energy nothing? What about quantum fluctuations, are...

I went on googling to find the answer to my last question, and got this: "The electromagnetic force is transmitted between object by the exchange of photons." Is this true?

Your thread here gave me a more preise possible image about our Universe... i wrote about it here: https://www.physicsforums.com/showthread.php?t=687860

I am no physicist either but I do lurk a lot and read, posting questions too. On top of what was said so well I'd like to mention few things to ponder about our Universe and possible realities and I know I'll get corrected as needed (these ideas are not mine, just may way of...

You are all great people because you take the time to share, and help explaining... Missunderstandings do happen, let's leave em behind... Thanks again to all!

Thank you very much for all your explanations. I think I have a bit better understanding about this topic now (room to improve it is enormous ;-) Would be interesting to see if we run a sophisticated computer simulation of Universe (from Big Bang onwards) long enough, if (self-aware) life...

I'd like (hope it counts as a fantasy world, or is too close to reality? hehe) to experience meeting allien races like in Star Trek (probably would first need my IQ to be boosted over 200 lol)

I learned too from this thread :) thanks all. I hope I don't ruin it now with this 'exotic' question: first, let me sumarise what I understood: in a free fall near a massive object like Earth or Sun we feel no weight and no force, we are falling towards the centre of that object due to...

Excelent diagrams.

I am getting confused now. Is C phsically maximal possible speed for anything in motion in Universe or is it just our definition/convention? You can not accelerate a massive object to C, but theory doesn't prevent possibility that it can start at C or at higher speed? (Not my idea, I read it...

So if we had some absolute frame of reference (so to say a viewpoint outside of Universe - please allow me this hypothetical situation, and let's say we have a rod of 1 meter for measuring distances anywhere in Universe), the physical space of our solar system would be different depending on two...

Thanks for another informative reply. Not sure yet how to imagine 'physical reality' with keeping in mind that physical 3D space changes depending on own speed relative to speed of C. As it's my bed time just one quick comment/question: but it is possible for a particle, say electron, to...

I thank you very much for taking the time to answer me with all the details. (especially post #22) I am still trying to understand it all, so pardon my ignorance if/as it arises. What I don't get is how can light from Sun to Earth take 499 seconds or 70.6 seconds depending on FOR, when the...

See post #17 pls.

The most interesting thing to me is that spacetime (distances) physically/really contract/shorten the more the faster you move... So in my example above, what is the distance from Sun to Earth for a spaceship traveling that path at speed 0.99 of C?

The average distance from the Earth to the Sun is 150 million km, so, what is it for that spaceship traveling at 0.99 C? Is it simply 0.01 of that distance? And for light (photon viewpoint) it is 0? (Since time for photon is 'frozen'.)

(I hope me question will make sense.) Right at the time spaceship traveling at 0.99C passes Sun, going towards Earth, the pilot starts measuring how much time it takes for light from Sun to reach Earth. Observers on Earth measure about 8 minutes and 19 seconds, does the pilot measure the...

And what would happen if there were no upper limit for motion? How would nature 'behave'? We still have that exception of spacetime expanding, where expansion itself can go faster than the speed of light/gravitation... So, if there is a star 'riding' such expansion wave, would that star go...

Sure, but not all 'why' questions make sense.

Couldn't the answer to 'why' be: because that's maximal speed 'fabric' of vacuum (empty space with quantum fluctuations) 'allows' photons (electromagnetical waves) to propagate?

OK thanks, I think I get it a bit better now. Though, if most consider that whole (not just observable) Universe is infinite then there is nothing strange if the scale of curvature of observable Universe is really large, right?

I can 'visually' explain this to myself only if I 'imagine' more dimensions than those we are able to perceive, and that Big Bang and expansion of Universe has to do with changes within dimensions (their 'relation'; maybe Big Bang was an event where other dimensions curved into themselves and...

So, our Universe (at least observable one) is a nicely formed sphere (it's not flat and it's not ellipse)?

From images it looks like observable Universe is far from expected 3D sphere, it looks more like 2D ellipse. So, why is it flat?

Well, I guess current science says that space and time are not separate, but one 'thing' as spacetime. Barbour has different opinion though, that time doesn't really exist, that time is merely our perception of motion of all things.