Topic: Request for clarification concerning universe expansion

[sweetandy]

My dad's really into astronomy and cosmology... sometimes some of the things he says are pretty woo, but overall he just likes reading popular science books on the topic.

Anyway, he insists that every point in the universe is moving away from every other point in the universe. I thought this sounded plausible, except I was wondering... on what scale? Would that apply to the cells in our body, or is each astronomical mass one of those "units" moving away from each other?

He tried to use this to refute that the Milky Way and Andromeda Galaxy would ever collide, even though as I understand it, that's a scientific fact. Can somebody set me straight on this?

[Chew]

My dad's really into astronomy and cosmology... sometimes some of the things he says are pretty woo, but overall he just likes reading popular science books on the topic.

Anyway, he insists that every point in the universe is moving away from every other point in the universe. I thought this sounded plausible, except I was wondering... on what scale?

On every scale not affected by gravity or the other forces. But it's slow. For every 3.26 million light years distance the universe is expanding at about 70 km/s (the Hubble constant). To put that number closer to home, for every 45 light years the universe is expanding at 1 meter per second. Not a lot, but the universe is very big. But remember, a lot of things are gravitationally bound. Our Solar System is not expanding (well, it is since the Sun is losing mass which causes the planets and asteroids to slowly spiral outward, but that is an orbital mechanics thing, not an expanding universe thing). Our galaxy is not expanding because it is gravitationally bound, the Milky Way galaxy has satellite galaxies that are gravitationally bound, clusters of galaxies and superclusters of galaxies are gravitationally bound.

Would that apply to the cells in our body,

No. They are held together by the electromagnetic force.

or is each astronomical mass one of those "units" moving away from each other?

He tried to use this to refute that the Milky Way and Andromeda Galaxy would ever collide, even though as I understand it, that's a scientific fact.

True. The Andromeda galaxy is blue shifted. We will collide in a few billion years.

[sweetandy]

On every scale not affected by gravity or the other forces. But it's slow. For every 3.26 million light years distance the universe is expanding at about 70 km/s (the Hubble constant). To put that number closer to home, for every 45 light years the universe is expanding at 1 meter per second. Not a lot, but the universe is very big. But remember, a lot of things are gravitationally bound. Our Solar System is not expanding (well, it is since the Sun is losing mass which causes the planets and asteroids to slowly spiral outward, but that is an orbital mechanics thing, not an expanding universe thing). Our galaxy is not expanding because it is gravitationally bound, the Milky Way galaxy has satellite galaxies that are gravitationally bound, clusters of galaxies and superclusters of galaxies are gravitationally bound.

I knew I came to the right place. Thank you immensely for your response, you've given me a great starting point to learn more about this.

True. The Andromeda galaxy is blue shifted. We will collide in a few billion years.

Concerning red and blue shift... my main exposure to these ideas was through a simple explanation in the Joe Haldeman book "The Coming". In it, there was an object on the verge of entering the solar system that they noticed was blue-shifted and heading right toward us... eventually discovered to be a ship.

For some reason, the thought of applying this principle to an entire galaxy... blows my mind. Thanks again!!

[Bastard Soap]

A friend of mine who's studying astronomy told me they prefere to talk about it as space getting more curved rather than actually expanding, not sure if it's just maths or there's really something to it.

[Trinoc]

A friend of mine who's studying astronomy told me they prefere to talk about it as space getting more curved rather than actually expanding, not sure if it's just maths or there's really something to it.

Surely less curved as it expands, not more. Think of the 2-dimensional analogy of an inflating balloon.

[Xptical]

Doesn't the Big Rip theory suggest that, since the rate of expansion is increasing, it will eventually overtake gravity, electro-magnetism, and the strong/weak nuclear forces?


Put another way, our atoms aren't currently moving away from each other *very* much, but it is happening.

[Traveler]

Doesn't the Big Rip theory suggest that, since the rate of expansion is increasing, it will eventually overtake gravity, electro-magnetism, and the strong/weak nuclear forces?


Put another way, our atoms aren't currently moving away from each other *very* much, but it is happening.

I have noticed that my mailbox is farther away every year.

[Alex Simmons]

For some reason, the thought of applying this principle to an entire galaxy... blows my mind. Thanks again!!

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

Physics of this apply to anything emitting a wave form that also has a motion relative to the observer.  From galaxies (and galactic clusters), to bees buzzing past your ear. 

It's a exceptionally useful means to assess the relative speeds of astronomical objects.  You can even use it to determine the rotational velocity of objects within a galaxy, as the opposite edges of a galaxy that's mostly side on to us will have a different amount of red/blue shift.

[Bastard Soap]

A friend of mine who's studying astronomy told me they prefere to talk about it as space getting more curved rather than actually expanding, not sure if it's just maths or there's really something to it.

Surely less curved as it expands, not more. Think of the 2-dimensional analogy of an inflating balloon.

No more curved, imagine you have a straight road, then imagine you are being forced to take a curved path, the distance will be larger. Things seem farther away because light is also taking this curved path. It sounds weird to me too but if you think about it they do seem analogous.

[Shibboleth]

Here is a question that is bugging me and I am sure it is because my mind can only wrap itself around 3 dimensions. They say that there isn't a center to the universe but if the universe is flat how is that possible. If the universe doesn't loop back on itself, "like the dots on an expanding balloon example" how is there not a set of edges to the universe?

[Trinoc]

A friend of mine who's studying astronomy told me they prefere to talk about it as space getting more curved rather than actually expanding, not sure if it's just maths or there's really something to it.

Surely less curved as it expands, not more. Think of the 2-dimensional analogy of an inflating balloon.

No more curved, imagine you have a straight road, then imagine you are being forced to take a curved path, the distance will be larger. Things seem farther away because light is also taking this curved path. It sounds weird to me too but if you think about it they do seem analogous.

Do you have a reference for this? It doesn't seem right to me.

[Bastard Soap]

A friend of mine who's studying astronomy told me they prefere to talk about it as space getting more curved rather than actually expanding, not sure if it's just maths or there's really something to it.

Surely less curved as it expands, not more. Think of the 2-dimensional analogy of an inflating balloon.

No more curved, imagine you have a straight road, then imagine you are being forced to take a curved path, the distance will be larger. Things seem farther away because light is also taking this curved path. It sounds weird to me too but if you think about it they do seem analogous.

Do you have a reference for this? It doesn't seem right to me.

I'll ask him, it does seem like just maths to me as I don't know how that would work in reality but alas reality rarely gives a shit about being weird.

[Bastard Soap]

Here is a question that is bugging me and I am sure it is because my mind can only wrap itself around 3 dimensions. They say that there isn't a center to the universe but if the universe is flat how is that possible. If the universe doesn't loop back on itself, "like the dots on an expanding balloon example" how is there not a set of edges to the universe?

Think of the balloon, as it was deflated every dot was the center cause it was one clump. As it started expanding every dot started moving away from every dot so it's impossible to say which is the center. If you did know the complete shape of the universe (which you never will be able to do because things move away faster than the speed of light) you could find the center of the universe by geometry. At least that's my understanding.

[Old Earth Accretionist]

Here is a question that is bugging me and I am sure it is because my mind can only wrap itself around 3 dimensions. They say that there isn't a center to the universe but if the universe is flat how is that possible. If the universe doesn't loop back on itself, "like the dots on an expanding balloon example" how is there not a set of edges to the universe?

Think of the balloon, as it was deflated every dot was the center cause it was one clump. As it started expanding every dot started moving away from every dot so it's impossible to say which is the center. If you did know the complete shape of the universe (which you never will be able to do because things move away faster than the speed of light) you could find the center of the universe by geometry. At least that's my understanding.

Or perhaps the centre of mass might be possible to find... but with space itself being infinite I'm not sure you can meaningfully define a geometric "centre".

[Anders]

Here is a question that is bugging me and I am sure it is because my mind can only wrap itself around 3 dimensions. They say that there isn't a center to the universe but if the universe is flat how is that possible. If the universe doesn't loop back on itself, "like the dots on an expanding balloon example" how is there not a set of edges to the universe?

Think of the balloon, as it was deflated every dot was the center cause it was one clump. As it started expanding every dot started moving away from every dot so it's impossible to say which is the center. If you did know the complete shape of the universe (which you never will be able to do because things move away faster than the speed of light) you could find the center of the universe by geometry. At least that's my understanding.

Or perhaps the centre of mass might be possible to find... but with space itself being infinite I'm not sure you can meaningfully define a geometric "centre".

I've heard that the centre is in 4-dimensional space, just like the center of the balloon is in 3-dimensional space but the dots are in 2-dimensional space.