What happens to light when it reaches the edge of the universe?

cangus

if this was the case, would the darkness of space even exist? wouldnt there be everlasting light in every single direction at every single point of time?

Thor

What happens to the value of a fraction as its denominator approaches infinity? This is the same thing that happens to light - but at a rate inverse to dist^2.

BTW...what makes you think the Universe has an edge? And what is on the other side of that edge?

Sariaht

I ment dr/dt ofcourse, pardon.

Matrixman13

I thought that with new experiments revealing the density of the universe it was exactly enough for a flat universe, not a curved one.

Nereid

In a closed universe, only if the expansion were slower than c.

Nereid

The question as to whether the universe is open or flat is still ... open It shouldn't be surprising if this is still under some debate 50 or 100 years from now ...

Phobos

Not if the expanding universe was finite in age (light from distant objects may not have reached you yet).

Phobos

In a closed universe, you may get a situation like hitssquad mentioned (space being curved such that the light beam reaches its starting point and goes around again).

In an open or flat universe, space is infinite (or at least boundless), so there is no edge. Offhand, I'm not quite sure how that works at the instant following the Big Bang...infinite space from the very beginning I think (or a temporary closed topology?)

In any of the models (closed, open, flat) there is no edge. The Big Bang was not an explosion of matter/light/energy into empty space. It was the rapid expansion of all of existance.

The Big Bang happened about 13.7 billion years ago & due to the finite speed of light, we could see the Big Bang if we could see 13.7 billion light years away (we can get close with current technology, but not that close). But if we were to magically transport ourselves 13.7 billion light years away, we would not be in the middle of the Big Bang. Things would look there as they do here because time has passed there too.

jcsd

An infinite unievres must of always been infinite, at the big bang in an infite unievres, you basically have an inifte, but infinitely dense space, which expands (in other words becomes less dense).

The universe is flat within experimental error, no-one is ever going to be able to say it's completely flat as that means measuring it's curvature precisely. Many of the interesting new cosmologies that make the mainstream media, (like for example the 'soccer ball' universe) have a curvature that is within the experimental error of the measured value, but are not flat. Flat unieverses needn't be infinite in space, howver I've been told that topologies which give flat finite universe are extremely non-trivial so the bog-standard infinite topology must be preferred.

The problem with phrases like an 'open universe' is technically it refers to a Friedmann-Lemaitre universe whioch is infinite in space and with either negative or Euclidian (i.e. no) curvature, that will contiune to expand forever. An open universe is an example of an 'open space' which is a infite space with no boundaries. It's gets even more confusing as people sometimes use the word 'open', rightly or wrongly to refer to other kinds of cosmologies that shares certain features with a Friedmann-Lemaitre open universe.

geometer

It is possible for objects in the visible universe (with respect to some obsever) to have recession velocities faster than the speed of light,...

This is a little confusing to me - I thought it was not possible for any object with a real rest mass to have a velocity equal to the speed of light, let alone exceed it.

Nereid

Take a look in the General Astronomy & Cosmology sticky (A&C reference library); there are several papers which cover this topic, in considerable detail. Look for "Lineweaver".

Flatland

What do you not understand? The universe has no edge, regardless if it's closed or not.

jcsd

There's a difference between velocity and recession velocity, it's only in special relativity that the observed velocity will be the same as the relative veloctiy with respect to c. In general relativity your dealing with spaces that aren't Euclidian and that have a dynamic geometry and special relativity becomes the local case only. Recession velocity isn't due to any actual movement of the objects themselves, but the expansion of spacetime, so there is no barrier to it being greater than c.

meemoe_uk

Space curvature is nice, but to really understand how things work you need to know whats going on at the quantum level, which is anyones guess.

meemoe_uk's law is a simple idea which deals with the edges of space with QM.
- every traveling quantum must have a start and end point
so no light can be sent off the edge on an infinate journey.

Quasars are the most distant objects we can detect, so they are our current best bet for 'objects on the edge'. By meemoe_uk's law, all their radiation must be transmitted back into the universe. This of course makes them seem to radiate much more intensely then we'd expect if we thought their radiation was free to fly off in any direction. Also this may explain why the universe appears to expand. Galaxys and quasars effectively have radiation thrusters which accelarate them into the least dense space, in the case of quasars this is off the edge of the universe! lol

Thor

Some people tend to overlook the fact that the very premise of their argument is flawed. Be patient.

Chronos

there is no 'edge' of the universe. only spatially bound objects have edges and the universe in not an 'object'.. it is all of spacetime. to think of it as an object requires the existence of non-object regions [i.e. spacetime continuums that originated independent of our universe]. it also requires them to interact [have observable effects] with this universe to be of any theoretical consequence. we have not yet observed any phenomenon in this universe that require the existence of other universes to be explained.

there is however a theoretical limit to the observable universe. hubbles constant predicts objects at a distance around 15 billion light years would be receding at the speed of light. we could therefore say the observable universe is a sphere 30 billion light years in diameter. of course, you would arrive at this same conclusion no matter where you were in the universe. this imaginary edge only exists in your local reference frame. under general general relativity, no matter where you are or what speed you travel, the 'edge' of the universe will always appear to be 15 billion light years [according to whatever clock you happen to have along] away from your current position. the long and the short of it is you cant get there from here, or from anywhere else for that matter.

marcus

Chronos you might enjoy reading "Expanding Confusion" by Tamara Davis. I will put a link, in case you want to.
http://arxiv.org./abs/astro-ph/0310808
It addresses some misconceptions about the expansion of the universe and the dimensions of what is observable.

You are right that there is a bound to the observable universe. But I dont think it is 15 billion LY.
Hubble's parameter has not been constant over time.
One cannot go by the present value of it.

Indeed, it turns out that
the light reaching us from many of the galaxies we see now was emitted at a time when that galaxy was receding from us at faster than the speed of light---and yet the light managed to reach us, curiously enough.
The Davis and Lineweaver article explains how this can be.

For example, galaxies are routinely observed at redshifts greater than 3.

In fact, one was recently detected to have z = 10 (by Roser Pello's group).

A galaxy observed at z = 3 must have been receding from us, at the time it emitted the light we are now receiving from it, at a speed greater than light.

using the standard "Sky and Telescope" calculator at S. Morgan's website
http://www.earth.uni.edu/~morgan/ajj...gy/cosmos.html

you can see that a galaxy observed with z = 3 would have emitted the light
when it was receding at 1.6 times c
and it would now be at a distance of 21 billion LY
and currently receding at a speed of 1.5 times c.

If you want to use the online calculator, put in 0.73 for dark energy (lambda)
and 0.27 for matter (omega), and z = 3 or whatever you want the redshift to be.

BTW it looks like you, flatland and Thor are all saying no edge to the U
and I can only say amen to that! I'm not certain myself there is even a back fence in the time direction , but for sure nobody I know thinks theres a spatial boundary