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-- the expanding universe - someone please explain?

the expanding universe - someone please explain?

how does infinite space stretch or shrink?

please use analogies and explanations in words rather than formulas, thanks.

if no one can be bothered, just let me know and i'll go hunting the web for information, just rather hear it from you guys.

do you mean how is it expanding?

either way, i dont have a clue good question tho. i hope someone here can help us both out. quantum physics ftw!!

The big bang happened. All the matter in the universe expanded outward at a constant rate. It is still expanding now. Imagine a single point in space, the origin of the universe. Everything is moving away from that point. It has 3 options in the future:
1) It will keep expanding forever because the outward force is more than the gravitational pull of everything
2) It will stop expanding and start collapsing. The gravity of everything is stronger than the outward force.
3) Gravity and outward force will equal eachother and the universe wont move.

Nothing we need to worry about though... unless you plan on living a LONG LONG TIME

quote:

Originally posted by Sunsnail The big bang happened. All the matter in the universe expanded outward at a constant rate. It is still expanding now. Imagine a single point in space, the origin of the universe. Everything is moving away from that point. It has 3 options in the future: 1) It will keep expanding forever because the outward force is more than the gravitational pull of everything 2) It will stop expanding and start collapsing. The gravity of everything is stronger than the outward force. 3) Gravity and outward force will equal eachother and the universe wont move. Nothing we need to worry about though... unless you plan on living a LONG LONG TIME

i can understand relative distance between entities growing, but if there were no entities in the universe, would it still be expending? how would one be able to discern that? (not sure discern is the right word, but hopefully you understood my meaning)

how can something with no end grow? where does it grow to? (same goes for shrink)

Think of three dimensional space as if it were a 2-dimensional point on the surface of a sphere, or the surface of the Earth if you will. One has infinite space on Earth in the sense that you can keep walking around and around and never reach a cliff or an "end". It is in a sense infinite. Now think of this three dimensional space on the surface of the Earth as the Earth expands or shrinks. You still have infinite space but it is expanding or shrinking. It's a little difficult to envision because our perceptions are limited to spatial geometry in 3 dimensions, but I believe that's the best analogy I've heard.

excellent analogy occ.

quote:

Originally posted by Sunsnail 1) It will keep expanding forever because the outward force is more than the gravitational pull of everything 2) It will stop expanding and start collapsing. The gravity of everything is stronger than the outward force. 3) Gravity and outward force will equal eachother and the universe wont move.

well, the rate or speed of expansion is increasing, so i dont reckon #2 also known as "the big crunch" will happen (yeah, me with my awesome command & understanding of science and all )

quote:

Originally posted by pkcRAISTLIN excellent analogy occ. well, the rate or speed of expansion is increasing, so i dont reckon #2 also known as "the big crunch" will happen (yeah, me with my awesome command & understanding of science and all )

Ah, well I haven't really been up to date on this stuff. What I posted above was off the top of my head.

quote:

Originally posted by Psy-T if there were no entities in the universe, would it still be expending? how would one be able to discern that?

As far as I understand, no.

You might want to read

http://www.amazon.co.uk/exec/obidos...9255026-6368720

It tries to be a laymans explanation of stuff like this.

When people say "the universe is expanding" I do not believe they mean that the nothingness area is expanding. When I say "the universe is expanding" I am implying that the matter that makes up the universe is spreading further apart. The space that this matter can go into is limitless because there is nothing there. What is going to stop matter from expanding?

quote:

Originally posted by Sunsnail Ah, well I haven't really been up to date on this stuff. What I posted above was off the top of my head.

hey, dont listen to me!! im happy to repeat stuff ive heard being said by people like hawking, but half the time im not sure if i understand it to begin with

theoretical physics is so far beyond me, but fuck i love it anyway actually regular physics is also too hard. well to be honest i failed parts of grade 9 (15yo) science ill have to admit. speak slowly people

quote:

Originally posted by Sunsnail When people say "the universe is expanding" I do not believe they mean that the nothingness area is expanding. When I say "the universe is expanding" I am implying that the matter that makes up the universe is spreading further apart. The space that this matter can go into is limitless because there is nothing there. What is going to stop matter from expanding?

i think i get what you mean. and i think i agree. i still cant really comprehend the nothing bit though.

and wtf is an entity?

quote:

Originally posted by Sunsnail All this has to do with variable constants. According to this school of thought light travels at a fixed velocity therefore it is constant...unless light travels through water or a vacuum then does that figure change..hence variable constant. Another oxymoron.

theres some aussie scientist now trying to prove that the theory of relativity isnt correct. hehe, ambitious.

we know gravity can bend it, but how does a vacuum effect the speed of light?

i want my own black hole

quote:

Originally posted by Sunsnail When people say "the universe is expanding" I do not believe they mean that the nothingness area is expanding. When I say "the universe is expanding" I am implying that the matter that makes up the universe is spreading further apart. The space that this matter can go into is limitless because there is nothing there. What is going to stop matter from expanding?

Actually I don't think the matter itself is expanding outwards. Sure matter moves in space but that movement is dictated by gravitational effects. However, there isn't a gravitational field coming from all directions that is pulling matter outwards (I think that would result in some heavily skewed elliptical orbits or something) rather I think that space itself is expanding and the matter is going along for the ride. Think of matter as 2 pen dots on a rubber band which is "space". As the rubber band stretches, the 2 dots do not move on the rubber band but rather "space" moves, contorts, whatever, and brings the dots along with them. Thus space is expanding ... which really cannot be classified as nothing despite the fact that there might not be matter in it.

quote:

Originally posted by pkcRAISTLIN we know gravity can bend it, but how does a vacuum effect the speed of light?

The speed of light in constant in different mediums. In a vacuum the speed of light is c, which equals 299 792 458 m / s. Yet in other mediums, such as water, glass, or air, the speed of light is less. Yet within each of those mediums the speed of light is constant. This is basically how fiber optics work, since light moves slower in glass it tends to stay within it. The light "bends" to follow the glass as that provides the path of least resistance.

And to stay on topic:

Have you read the Ultimate Hitchikers Guide to the Galaxy? There is another interest conundrum about the infinite nature of the universe:

The books states that the population of the universe is 0. This is becuase there are an infinite number of planets in the universe and there are only a finite number of populated planets. Therefore the ratio of populated planets to unpopulated planets is 0 since any finite number divided by a infinite number is 0.
I always like that one.

quote:

Originally posted by occrider Actually I don't think the matter itself is expanding outwards. Sure matter moves in space but that movement is dictated by gravitational effects. However, there isn't a gravitational field coming from all directions that is pulling matter outwards (I think that would result in some heavily skewed elliptical orbits or something) rather I think that space itself is expanding and the matter is going along for the ride. Think of matter as 2 pen dots on a rubber band which is "space". As the rubber band stretches, the 2 dots do not move on the rubber band but rather "space" moves, contorts, whatever, and brings the dots along with them. Thus space is expanding ... which really cannot be classified as nothing despite the fact that there might not be matter in it.

I see what you're saying actually. I do not understand, though, the force that is pulling matter outwards. What keeps the matter from just staying where it is while space is expanding

quote:

Originally posted by Sunsnail I see what you're saying actually. I do not understand, though, the force that is pulling matter outwards. What keeps the matter from just staying where it is while space is expanding

if i understood properly, it's the energy of the inital big bang, the continuation of movement, that force

quote:

Originally posted by Psy-T if i understood properly, it's the energy of the inital big bang, the continuation of movement, that force

Well, that's what I originally thought with my first post. Then occrider says that it matter isn't actually moving, the space is.

quote:

Originally posted by Sunsnail Well, that's what I originally thought with my first post. Then occrider says that it matter isn't actually moving, the space is.

oh sorry, i misread your question before

i dont have any problem envisioning it, especially with the help of the rubberband analogy, though i doubt i can explaing it any better, so i wont try

I actually did a presentation once on this a long time ago. Stephen Hawking has done some work to support the theory that the universe either achieves a critical point and continues to expand indefinitely or it achieves a critical point where its internal gravity ultimately pulls everything back in and the universe eventually collapses back into a singularity (or something like that)--think rubber bands...

One thing in particular that I remember is that scientists have physically observed the Doppler Effect from other interstellar bodies, which proves that bodies are moving futher away, i.e. the universe is "expanding". Although, yeah, conceptually it doesn't seem logical that an "infinite" amount of space could somehow grow or shrink, since by defnition, infinite would already occupy all available space, all the time.

If you're really curious about some of this stuff and haven't already watched it, go check out Hawking's A Brief History of Time. I'd probably recommend the movie over the book. Neither are terribly exciting, but should at least give you some answers (even if they are only theoretical).

thanks everyone

Just want to add a few things:

quote:

Originally posted by Sunsnail The big bang happened. All the matter in the universe expanded outward at a constant rate. It is still expanding now. Imagine a single point in space, the origin of the universe. Everything is moving away from that point...

This is incorrect in the sense that the Universe didn't expand from a single point. The Big Bang was like an explosion OF space, not an explosion IN space. Therefore it happened everywhere at the same time, there is no centre to the Universe.

quote:

Originally posted by Shakka One thing in particular that I remember is that scientists have physically observed the Doppler Effect from other interstellar bodies, which proves that bodies are moving futher away, i.e. the universe is "expanding".

Just nitpicking here. The redshifts that astronomers are not due to the Doppler Effect. The galaxies are not moving away from us (which would cause a Doppler shift) but rather it is the space between us that is expanding. The effect is pretty much the same though, but the implication is different. If the galaxies were moving away then that would imply that there is space to move into.

As for questions about matter being pulled apart, think of the expansion of the universe as being caused by a force (known as Dark Energy, the cause of which is still debated). In a galaxy, or a cluster of galaxies, the amount of mass causes enough gravitation to match the pressure of expansion and you get an equilibrium. Between clusters, the distances are too great for gravity to be able to overcome expansion.

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