Speed of light and expansion of space

Post Reply New Topic

Hi.

I am reading about relativity. After years of reading about I am still not clear on whether I understand it or not

I just have a question to pose. It might be that I am thinking and talking bollocks here but please give me your opinion on my query.

We say that space is expanding at a faster rate than the speed of light. So light from distant galaxies will never reach us. So in the night sky we see lots of black space. But if space started to expand at a slower rate than the speed of light or even started to contract, and then we looked up at the night sky. I am wondering if we would suddenly see lots of new galaxies appearing as time moved on. So each night when we looked out we would find new galaxies. After many days perhaps the sky would be so littered with new galaxies that the night sky would appear brighter and brighter...?

Is this a valid thought I am having?

Also what would happen with time in this scenario? Would time start to run slower or even backwards as Stephen Hawking implies in a Breif History of Time.

Does anyone understand this or does everyone (like me) just take their word for it?

let me preface this statement by saying i am no rocket scientist like some of the other posters here on this forum. that said, i remember hearing a while back, that because of the recession of the furthest reaches of space beyond our technology of perception, that the actual distance to the event horizon [birth of the this universe] measured in light years is not merely [approx.] 14 billion light years but closer to 45 billion light years. i have no idea how this was figured out.

I fundamentally question the claim of the universe expanding faster than the speed of light. As no mater can move that fast (supposedly) then it is fundamentally flawed.

I can accept that the limit of how far we can see defines the edge of the "visible universe" but how do they know how much is beyond that?

The universe is, insofar as we can perceive, a four dimensional manifold, although theories have attributed as many as eleven dimensions to it. If it is a hypersphere with the radius in the time dimension we and all matter exists on the surface of that expanding four dimensional sphere.and perhaps light and matter is limited in travel on that surface. But the universe itself may not be so limited in expansion velocity. I don't know.

i have never read anything about it so my contribution is entirely based upon my own conjecture and is almost certainly incorrect. i have not the ability to read or be taught things other than basic instructions because i can not contextualize external words well.

anyway, if there is a boundary where space ends, and there is no space beyond that boundary, and if i am at that boundary and i try to travel outward, then will i hit a wall of existence that can not be passed ? no i will not, because if that wall is traveling at faster than the speed of light away from where i am, then even if i was to travel at the speed of light toward it (which is impossible for matter), it would recede from me faster than i approach it.

if space can expand at a speed faster than light, then it must not be material, and if it is not material, then it is also not related to energy which is the essence of matter.



that is if it is assumed that the material existence of galaxies is carried away with the expanding space they exist in at a speed greater than light speed so that their light will never reach us. if the galaxies are carried outward with the expanding space at faster than the speed of light (relative to our location), then it must not be true that the speed of light is the universal speed limit because those galaxies are receding from us at a speed faster than the speed of light.

one may say that the speed of light is relative to the space it travels in, and that if that space is expanding, then the speed of light emitted from those galaxies will be reduced as it shines back in our direction, but i believe the speed of light is constant without regard to relative motion in time.

let us say that you suddenly travel away from me at the speed of light and then switch a torch on and shine it at me. it is an easy trap of thought to fall into where one may consider that because you are traveling away from me at the speed of light, that the beam of light which is shining from your torch to me also at the speed of light will never reach my eyes because your outward bound velocity matches the speed of the light shining from your torch, and therefore it will cancel the approach velocity of the light from your torch to my eyes in the same way as if you threw a ball at me at 30 mph from the back of a truck traveling at 30 mph away from me would appear stationary to me and fall to the ground at the point where you threw it.

but i do not believe light is associated with time at all.

let me put it this way. if you break down (let's say) the first second after you begin traveling away from me at the speed of light and switch your torch on, into an infinite amount of "instants".
because an instant has no duration, the whole passage of time is frozen within each instant. that means that at each instant, you are not moving at all, because if i could see you in one instant as you were traveling away, you would be stationary. but light would also be shining from your torch unaffected by the stoppage of time, and the light from your torch that left it at that instant while you were stationary in time would travel at the speed of light toward my eyes, therefore it would reach my eyes at the speed of light.

i know that doppler shifting would make it redder of bluer, but that is only a function of frequency rarefactions or compressions of amplitudes of the manifestation of light, and not the essence of the energy of light that is instantaneous.

and then tweety got sylvester's tail hammered by a falling window sill.

i know what i said is primitive, but it is at least a contribution to this otherwise unaddressed thread.

You exist in four dimensional space on the three dimensional surface of a four dimensional sphere. Space folds back on itself. There is no "wall". You are the equivalent of flat Earther worrying about falling off the edge. Just as Earth has no edge, the universe has no wall.

The speed of light barrier only applies to matter and energy moving through space, not space itself. Also, the generalisation of the principle of relativity to curved space-times means that the principle applies locally but not necessary globally. In other words, light and and matter a great distance away from us, at least when calculating it at distances beyond the horizon, may appear to us to us to be travelling faster than light but it does not violate this principle because relative to anything in that region of space, motion will always be slower light. You can show this mathematically by constructing light cones at any point in the space.

14 billion light years would be how far the light has travelled to get to us. The larger number would be how far the point that the light originated from originally is from us at this moment.

The entire time the light has been travelling, the universe has been expanding in all directions.

It might help to imagine an ant walking along the surface of a balloon that is slowly being blown up. 14 billion light years corresponds to the speed times time of the ant, the 45 billion light years would correspond to the length of a line drawn on the balloon at the present time.

That would be true only if space-time were spherically symmetric which it is not. Spacetime is not a four dimensional hypersphere. It is either flat or slight negatively curved.

ruveyn

According to http://en.wikipedia.org/wiki/Shape_of_the_Universe the curvature of space is yet to be determied.

ah so
thank you for that carl saganesque explanation which even i can understand. and all us humans and our co-earth-residents are as but ants in the grand scheme of things.

I like to use the example of a loaf of raisin bread.

When you first make the dough, it is small, and the raisins are all fairly close together. As the dough rises, the "universe" expands and the raisins are all moving away from each other.

In our universe, we know all the galaxies are moving away from us. That does not mean that our galaxy is the center of that expansion, but merely that we are one "raisin" in the loaf that is expanding uniformly.

Now if we believe that the universe began from a single, infinitely hot, infinitely dense point, then the existence of any physical universe beyond the Hubble Radius (approx. 14 bn light years) from the origin point would violate the principle that c represents an upper limit to the velocity of matter.

However, if the Big Bang merely represents the origin of the observable universe, then it is entirely possible that there are other Big Bangs happening in locations outside the Hubble radius, in a physical universe that is larger than the finite, observable universe that surrounds us.

The assumption seems to be we can see all galaxies.

space has 3 dimensions. a surface has only 2 dimensions since it has no depth. if you consider a sheet of infinitely thin paper, you may say that is is 3 dimensional if you bend the paper since it has co-ordinates in 3 axes, but the lack of depth means that it's volume is zero, and therefore it does not exist in reality, but only in concept.

anything that has zero volume is non existent.



i refuted the idea of a "wall" of existence in my previous post, so you are barking up the wrong tree.

my shortcoming is that i have not read the words of master thinkers on this matter like you have. unlike you, i can not parrot a recitation of the literature compiled by great thinkers.

i enjoy considering the universe from my own perspective, and it may be considered that so does a fruit fly, but who knows if a fruit fly somewhere in history suddenly figured it all out but was swatted in the next second, or lived it's live with no means of communicating it.

nothing is proven as yet. it is just that the minds that are the most revered have made proclamations, and the rest of the world reside in belief of those proclamations and relay them with reverence and fierce loyalty.

have you thought about it all on your own with no reference to anything you ever read? i would suspect not.

anyway, the answer to everything will not be discovered within this thread, and even if it was, it would never be able to be communicated.

The three possibilities for the shape of the universe are closed, open or flat. The closed universe, which is the one described by a hypersphere, has already been ruled out by the discovery that the expansion of the universe is accelerating. Plus the curvature of the universe has currently been measured to the extent that we can confirm that the curvature of the universe is very slight, at least on the scale of our observable universe. Ruveyn is correct, the universe is either open or flat and would have slight negative curvature in the case that it is open.