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The universe is expanding faster than expected

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Re: The universe is expanding faster than expected

#131

Post by pdonis »

mpoteat wrote: post #125
pdonis wrote: post #115

Earlier quoted context omitted.

> It would indeed be incredibly exciting if it would lead to a less silly explanation of the redshift than "universe is expanding". It won't. There is no question about whether the universe is expanding. The issue is over how fast it is expanding; we have two different theoretical models that are giving different answers, and we don't understand (yet) how to reconcile them.

Not a physicist, but why isn't the simple explanation that light loses energy over cosmological distances not also a valid explanation of redshift? We already know that energy isn't conserved at those scales.

> why isn't the simple explanation that light loses energy over cosmological distances not also a valid explanation of redshift?

It depends on what you mean by "light loses energy over cosmological distances". See below.

> We already know that energy isn't conserved at those scales.

This suggests that what you mean by "light loses energy over cosmological distances" is that the universe is expanding while the light travels, and in an expanding universe, total energy is not conserved. That is true, and that is the redshift due to the universe expanding--it's not something different.

If, however, you are working from the hypothesis that the universe is not expanding, then energy is conserved even over cosmological distances, so I don't understand what you mean by invoking "energy isn't conserved" as an explanation for the redshift.

If you're referring to the "tired light" hypothesis, that's been known to be unviable for decades.

Re: The universe is expanding faster than expected

#132

Post by ninkendo »

chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

> Can someone explain why the universe is expanding at all?

I think the answer to this is “no”. If you could properly ascribe a “cause” to the universe’s expansion (and could prove it), you would definitely be first in line for a Nobel prize, at the very least.

And no, “dark energy” isn’t an answer; it’s a placeholder term for that which we don’t understand about the universe’s expansion.

Re: The universe is expanding faster than expected

#133

Post by nuclear_eclipse »

chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

If you can answer the why, then I think physicists around the world would really like to know. We "know" the universe is expanding because we can observe the effects (eg, red shift of further away stars/galaxies), but the "why" has been the big, fundamental question for as long as it was predicted and/or observed. It's almost certainly related to some property of physics that we don't yet understand, but ultimately, we may never know any reason beyond "that's just how it is".

Re: The universe is expanding faster than expected

#134

Post by lisper »

User23 wrote: post #80
lisper wrote: post #72

Earlier quoted context omitted.

> why don't you please present me with both? If you are not a YEC, then the first thing I'm going to do is ask you why you think that cosmology and physics are different? If you are a YEC then I don't need to ask you that question because I already know the answer. (It's because you have accepted the truth of the Bible as a foundational assumption. From this, the idea that modern cosmology is not science is a logical…

If I were not a YEC, then I'd think cosmology and physics are different because physics is a laboratory science where depending on our budget we can do anything from roll balls down inclines to produce quarks while with cosmology we have absolutely no control over conditions and can only make believe we do by sampling in a way that necessarily is corrupted by our biases. And the amount of data to sample from is plent…

> physics is a laboratory science

That would come as news to most theoretical physicists, who rarely set foot in a laboratory.

> we can ... produce quarks

How do you know we can produce quarks?

Also, where does astronomy fit into your taxonomy? Was Newton doing science or phenomenology when he came up with the inverse square law? Plate tectonics? What about (drum roll, please) biology?

Re: The universe is expanding faster than expected

#135

Post by neom »

chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

Here are a series of episodes from PBS spacetime that explain Inflation and Expansion: https://www.youtube.com/watch?v=aPStj2ZuXug&list=PLKjJE86mQR...

Re: The universe is expanding faster than expected

#136

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Re: The universe is expanding faster than expected

#137

Post by burlesona »

7373737373 wrote: post #5

Here's a narrated video about this current cosmological crisis: https://www.youtube.com/watch?v=0sfvQ_fsil4 This is one of the key graphics: https://i0.wp.com/particlebites.com/wp-content/uploads/2020/...

Thanks for sharing! Seems like a good video but I don’t really enjoy long-form video... any relevant articles or written media describing the same thing?

Re: The universe is expanding faster than expected

#138

Post by mabbo »

chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

Thing about the big bang is that, as current theories go, it wasn't really an "explosion".

Take a rubber band- one of those big wide ones- and draw two dots 1cm apart. Then stretch the rubber band. The dots aren't moving, but the distance between them is growing. That's the big bang.

During the big bang, the distance between things increased at speeds faster than the speed of light. They didn't move at all (no FTL movement), just new space existed between everything. Still happening now, just at a slower pace (but a pace that seems to be increasing?).

Why? Answer that definitively and you'll earn yourself a Nobel prize or two.

Re: The universe is expanding faster than expected

#139

Post by gpderetta »

mpoteat wrote: post #125
pdonis wrote: post #115

Earlier quoted context omitted.

> It would indeed be incredibly exciting if it would lead to a less silly explanation of the redshift than "universe is expanding". It won't. There is no question about whether the universe is expanding. The issue is over how fast it is expanding; we have two different theoretical models that are giving different answers, and we don't understand (yet) how to reconcile them.

Not a physicist, but why isn't the simple explanation that light loses energy over cosmological distances not also a valid explanation of redshift? We already know that energy isn't conserved at those scales.

Energy is not conserved at those scales because of general relativity, which also provides the mechanism for an expannding universe. Einstein himself didn't like this result of GE and tried to hack around it with the cosmological constant. Turns out the math was right.

Re: The universe is expanding faster than expected

#140

Post by Rexxar »

chanakya wrote: post #126

Can someone explain why the universe is expanding at all? I've heard it said "it's the momentum from the Big Bang". That sounds reasonable, but then we're told that it's not that the galaxies are flying apart, it's that the "basic metric of space itself is expanding". I can understand momentum from an explosion, but why would "space itself" expand because of an explosion?

Science ultimately never answer to "why?" but to "how?". Science give us a model to describe universe but won't tell you why it exists.
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