What happens when a ray of light hits the boundary of the universe?

[marcus]

There are thin areas in the cosmic microwave background. It is not uniform in all directions. This means space cannot be infinite in all directions, for there would be infinite stars in all directions and light would be shining equally from all directions. right?

Your reasoning doesn't make sense to me.

The CMB is uniform to with one part in 100,000. There are what you call "thin" places, that is places where the temperature is about one thousandth of one percent less than average. The false color pictures exaggerate, of course.
In any case, that doesn't say anything about space being finite.

http://en.wikipedia.org/wiki/Cosmic_microwave_background

You haven't given us any reason that space couldn't be infinite in all directions, and approximately uniformly filled with matter (stars, galaxies, etc.)

Space might be either infinite volume or finite volume, we can't tell yet with the data we have so far.

Since the oldest stars are only about 13 billion years old, even if space were infinite volume uniformly full of an infinite number of stars we still would not SEE an infinite number of stars in the sky because finite age limits how far starlight can have traveled.
Even if space is infinite we are only in touch with a finite piece of it.

You might try reading up on "Olber's Paradox" It's not really a paradox, they just call it that for historical reasons. Try Wikipedia on it, might be OK.

 

[russ_watters]

In addition to the "thin" places not being very thin, they are not arranged in such a way as to suggest a direction for a center or edge. They are spread randomly and are very localized.

 

[SideReal]

Hmmm... the balloon you are speaking of is just an approximation of the Klein-bottle that is the real universe.

A Klein bottle is, effectively, a 4 dimensional spherical 'balloon.'

It's expanding. Or at least it looks like it is because astronomers have noticed that everything appears to be red-shifted away from us.

More accurately, it appears that all of the objects are accelerating towards something they have termed 'The great attractor' located somewhere in the Centaurus Supercluster. The Great Attractor is an anomalous mass weighing in at an approximated tens of thousands of Milky Ways.

Another theory, postulated by Senovilla is that the universe isn't really expanding so much, per se, as that time is literally slowing down. This argument has merit since the latest en vogue creation theory: Inflationism, indicates a period where the universe actually expanded superluminally. If you postulate that time is variable, however, you open the doors to allowing time to be passing at a much accelerated rate at the early stage of the universe and thus the expansion is still at or near light speed.

Everyone's question as to 'what would the edge of the universe look like' is non-sensical. What does the edge of the world look like? It doesn't, because there isn't one.

Therefore, to the OP's question: What would happen if a EM wave hit the edge of the universe? Nothing, there isn't an edge of the universe.

Just my 2 cents.

 

[SideReal]

There are thin areas in the cosmic microwave background. It is not uniform in all directions. This means space cannot be infinite in all directions, for there would be infinite stars in all directions and light would be shining equally from all directions. right?

No one on the forum has suggested that space is infinite. In fact, they have repeatedly said it is boundless and finite.

 

[cragar]

light would then circle the universe.

 

[cbd1]

Wow. That is true genius. Now I understand it.. The light circles the sphere, that way, no energy is lost from the system.

Thank you cragar

 

[cragar]

your welcome.

 

[stalon34]

light can never escape the universe simply because there is no space outside of our universe. so when light reaches the boundaries of universe it bends to one side.

 

[havonasun]

Finite, yet boundless. I think the confusion comes from trying to wrap a 3d brain around a tesseract. A point is flat. A line is flat. A plane is flat. By extension, we are flat. The 3d being rejects this because experience dictates otherwise.
There is a certain quantity of universe; that makes it finite. Yet, to be boundless, the 3d "plane" forms a sphere. The void (not space, space is 3d) inside and outside the sphere are one and the same; unseparated. The 3d mind interprets "sphere" as a ball, but this is a 4d thing - we wouldn't understand. That is why, a plane/line seems to curve as it moves away from the point of observation. It is still perfectly straight. The curvature is a pseudo-illusion. It's not really there, but it is still significant. As 3d beings, without our math instruments, the curvature is a sensory perception of 4d reality.
There is no boundary, just as a circle has no end.

 

[stalon34]

dear havonasun,

thank you for your reply, however i think you got the whole thing wrong; points,lines and planes are not flat. they are not 2D. in fact there is no such thing as 2D as apposed to our " 3D mind". 2D world is mathematical abstract. points, lines and planes are only mathematical concepts. every thing in this universe is 3D. and there is actually a boundary, but it depends on where you draw this boundary. if the universe that we see and perceive in any possible way through our instruments finishes at 13 or 15 billion light years around, then that is the boundary and light can never escape that. but one might ask what is beyond the boundary of this universe if we assume that there is a boundary. the answer is that because we and every thing else in our present universe is made out of the fabric of space and there is no space beyond our universe then it is impossible for us to imagine. we just simply say beyond is nothingness.

 

[cragar]

isn't everything in our universe 4d

 

[havonasun]

Stalon, that's where I got tripped up. It's a real paradox, its a boundary that is there but doesn't exist. The void or nothingness, by definition, can't be pointed to; you just end up pointing at the back of your head.

if the universe that we see and perceive in any possible way through our instruments finishes at 13 or 15 billion light years around, then that is the boundary and light can never escape that.

Until the following year when the Pro version comes out and then we can see 18 billion ly! That is the strangeness of this concept; light can't escape because there's nothing to escape. A beam of light will travel in a straight line through this universe for eons of eons and never reach the end. Its like Asteroids on Atari when your ship goes off the edge and appears on the other side of the screen.

I might still be wrong, everyone feel free to correct this.

 

[cragar]

A beam of light will travel in a straight line through this universe for eons of eons and never reach the end.

light would eventually come back around to where is was emitted .
There is a book called Mr. Tompkins in wonderland written by the physicist George gamow
and he talks about throwing a book off a planet and seeing it go away from the planet
it gets smaller and smaller as it goes away , then it starts to get bigger again then it appears as if it is right next to the person that threw it , he reaches out to touch it and he can't , because the lights rays are converging just like the meridian lines on our globe
when we see the imaginary image next to us the book is halfway around the universe
and then it eventually comes back to use , This would happen in our universe
it would just take a long time .

 

[havonasun]

Yep, that's what I meant. I love the mental visuals from paraphrase you gave. I think I'm going to look that book up.

 

[stalon34]

I just don't understand why havonasun keeps insisting on light traveling on a straight line. straight line is a very old and wrong concept. it has been proven that there is no such thing as straight line any where in universe due to the presence of gravity. if we accept straight line then we have to believe that our universe is a flat plane. while flat plane, straight line and point are only abstract mathematical concepts and not physical reality. every thing in universe is 3D; mathematical concepts are 2D. True way of knowing our universe is to collect the actual and factual observations and then allow these observations lead us towards imagining the unobserved aspects or features of our universe. In plain words, observe and then imagine the unobserved parts. What you guys are doing is quite the opposite. You guys plunge yourselves right at the start into a type of universe that is supported by nothing but your pure imagination.

 

[peterdorey]

It's all just movement in Stillness & stillness in Movement (a bit of Manhamudra there).
With e-m radiation "sloshing" around (this sentence loosley quoting ProfBECox seem to recall).

 

[Skaffen]

The only constant is change.

The Universe is 'Infinitely Bounded'. - Just as explorers (hundreds of years ago) thought there was an edge to the world, contemporary scientific observations lead us to think we have found the edge of the Universe...Dark Energy anyone?

From recent images (Keck, I think), the observable Universe appears to be an oblate sphere, which to me suggests it is spinning (Why not? Everything else does). This spin would imply a greater shearing force the further from the origin (Increased radius), hence the observed increased acceleration in spatial expansion over Time.

The balloon analogy invokes an inflationary process which does not address the principle of Conservation and consequently is misleading - a more useful description is to term it 'unfolding'...like an umbrella being spun.

Imagine a planet composed of a perfect liquid that is disturbed by a pebble (breaking symmetry) - the wave would reach the pole and make it's return journey 'indefinitely', however all is connected so the energy is transferred partially to another 'object' and the result/remainder is returned to the origin (feedback)..and evolves, becoming increasingly complex and diverse until it stabilizes through synchronisation.

Gravity is the tension of our liquid, light is the breaking of the wave.