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Webb and Hubble confirm Universe's expansion rate

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Re: Webb and Hubble confirm Universe's expansion rate

#91

Post by hughesjj »

hinkley wrote: post #74
rf15 wrote: post #53

Earlier quoted context omitted.

This, together with the endless philosophising around dark energy, dark matter and whatnot paints a pretty strong arrow towards our models having some flaws when it comes to their large-scale application. I hope to live long enough to see where we made our mistake and get a better model.

I still have $20 down on "We are living in a universe inside a black hole."

I mean effectively we are regardless. The cosmological event horizon is a thing.

Also, I forget off the top of my head, but there's some oddities depending on your chosen frame of reference when looking @ hawking radiation (skip to part about relativity of the vacuum) that I think could apply to the cosmic event horizon as well

https://youtu.be/isezfMo8kWQ?si=5m_L6JtZ7p7Ls6xH

Re: Webb and Hubble confirm Universe's expansion rate

#92

Post by sebzim4500 »

throwawaymaths wrote: post #85
tzs wrote: post #28

A little background based on a few articles about this plus my recollection of PBS Space Time videos on this: There are at least two ways to try to figure out the rate of expansion of the universe (which is called the Hubble Constant). • From variations in the cosmic microwave background (CMB) which are the result of certain conditions in the early universe it is possible to figure out what the expansion rate should…

There's a 'fringe' theory that the CMB is not the echo of the big bang but rather the redshifted black body radiation of intergalactic dust (apparently the numbers are about right). Although the primary proponent of this theory is trying to justify some sort of cyclic universe model with it, if my understanding is correct it would still be compatible with a 'standard' big bang that has the "longer" (aka galactic expa…

How could that be true?

Wouldn't that smear the spectrum so that it no longer so matches the black body radiation of a single object of a set temperature?

Re: Webb and Hubble confirm Universe's expansion rate

#93

Post by arbitrage »

westurner wrote: post #18

Hubble's law: https://en.wikipedia.org/wiki/Hubble%27s_law Expansion of the universe: https://en.wikipedia.org/wiki/Expansion_of_the_universe : > While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects Given that v is velocity in the opposite direction, and c is the constant reference fram…

Tachyons aren't a thing. Tachyons are sci-fi nonsense.

Nothing in the universe can travel faster than the speed of light. This does not hold for the universe itself. It can and does expand faster than the speed of light, using specific reference frames (i.e., big enough).

So, space can increase FTL. Particles do not travel faster than light tho, that is nonsense.

Re: Webb and Hubble confirm Universe's expansion rate

#94

Post by arcastroe »

digging wrote: post #72
arcastroe wrote: post #46

I've asked this question before, but I don't think I received a good answer, so figured I'd try asking again. How do we know that galaxies are accelerating away from us and not moving at constant speed? People often point to the observation that the further away a galaxy is, the faster it appears to be moving away from us, implying acceleration. However, wouldn't we expect to see the same observation even without any…

It's because the movement is ascribed to the expansion of space itself, not the individual galaxies. We don't have any reason to believe galaxies are moving in random directions at random speeds (not at scales that explain the redshifts we call the expansion of the universe). In your explanation, I think we'd expect to see some very distant, very slow-moving galaxies moving toward us. And there may be some very fast-…

> In your explanation, I think we'd expect to see some very distant, very slow-moving galaxies moving toward us

Thank you, but I suppose I'm not really questioning the big bang piece. My question was mostly in regards to the continued acceleration piece. Feel free to disregard the "in random directions" part of my original post.

I'm picturing more of an explosion in empty space. A firework or granade of sorts. Any individual dust/shard of the explosion still sees all other objects moving away from it and the rest of my question stands. But I suppose this would imply a "center" to the explosion, which I've also heard is not the case.

Theres a few other comments offering more clarity to the acceleration piece. Thank you everyone!

Re: Webb and Hubble confirm Universe's expansion rate

#95

Post by [deleted] »

tzs wrote: post #28

A little background based on a few articles about this plus my recollection of PBS Space Time videos on this: There are at least two ways to try to figure out the rate of expansion of the universe (which is called the Hubble Constant). • From variations in the cosmic microwave background (CMB) which are the result of certain conditions in the early universe it is possible to figure out what the expansion rate should…

[deleted]

Re: Webb and Hubble confirm Universe's expansion rate

#96

Post by not2b »

elashri wrote: post #63
db48x wrote: post #52

Earlier quoted context omitted.

No, we measure the frequency of vibrations of _light_, not of a type of atom. Specifically, it is light emitted by cesium atoms that are transitioning from one specific energy state to another specific energy state. Although this is arbitrary, it is highly reproducible and would give precisely the same measured lengths of time at any point since the big bang.

That assumes that fundamental laws of physics did not change (will not change). This is what we believe and have no evidence otherwise. This is important since we rely on measuring atomic transitions of cesium atoms which itself were formed/forming billions of years after the big bang itself. The laws of physics invariance under time is a core to our understanding. It would be very disrupting if we found otherwise.

Right, but most deviations one can think of (like, changes over time to physical "constants") would have an observable effect, so ancient galaxies would look much more different from modern galaxies and spectra wouldn't look the same other than a red shift, which moves all the lines in a uniform way.

Re: Webb and Hubble confirm Universe's expansion rate

#97

Post by pdonis »

arcastroe wrote: post #46

I've asked this question before, but I don't think I received a good answer, so figured I'd try asking again. How do we know that galaxies are accelerating away from us and not moving at constant speed? People often point to the observation that the further away a galaxy is, the faster it appears to be moving away from us, implying acceleration. However, wouldn't we expect to see the same observation even without any…

> How do we know that galaxies are accelerating away from us and not moving at constant speed?

More precisely, we see that galaxies started accelerating away from us a few billion years ago; before that they were decelerating (moving away from us but with the "speed" decreasing instead of increasing).

> People often point to the observation that the further away a galaxy is, the faster it appears to be moving away from us, implying acceleration.

That observation tells us that the universe is expanding, but by itself it does not tell us whether the expansion is accelerating or decelerating or neither. So you are correct that that observation alone is not sufficient to show that the expansion is accelerating.

What we look at to see how the expansion rate changes with time is a comparison of three pieces of observed data, galaxy by galaxy: redshift, brightness, and angular size. The relationship between these three quantities is what cosmologists use to construct a model of the expansion history of the universe, which in turn tells us things like what I said above, that the expansion has been accelerating for the last few billion years but before that it was decelerating.

Re: Webb and Hubble confirm Universe's expansion rate

#98

Post by not2b »

m3kw9 wrote: post #47

If we can travel faster than light does it blow up the theory that the universe expands? Because if we can travel faster than light the universe is theoretically be infinite if I can go to a point pas the furthest reaches of stars/matter.

If we can travel faster than light, that would blow up all the theories that say that we cannot. And FTL travel would imply time travel (if in your reference frame, something is traveling faster than light, there's another reference frame where it is going backwards in time). A lot of science fiction just sweeps this under the table and pretends that we have Newtonian absolute time to go along with the FTL travel.

Re: Webb and Hubble confirm Universe's expansion rate

#99

Post by dclowd9901 »

cowgoesmoo wrote: post #65
rf15 wrote: post #53

Earlier quoted context omitted.

This, together with the endless philosophising around dark energy, dark matter and whatnot paints a pretty strong arrow towards our models having some flaws when it comes to their large-scale application. I hope to live long enough to see where we made our mistake and get a better model.

We know for sure that there are issues with our current theories. Our two best theories, general relativity and quantum mechanics, are not compatible with each other. https://en.wikipedia.org/wiki/General_relativity#Relationshi...

Interesting to think we only got the “middle” size physics right, but we can’t reconcile it with micro or universal physics.

Re: Webb and Hubble confirm Universe's expansion rate

#100

Post by itishappy »

Veserv wrote: post #68
explaininjs wrote: post #26

Earlier quoted context omitted.

> Of course, all the results have error bars. Not to mention the underlying philosophical assumptions, such that the "rate of time" has been constant across all of... time. Aka: How do we know a "year" 13 Billion "years" ago bears any resemblance to one now? What would it mean for it not to?

Well for one, if the laws of physics are not time invariant (i.e. the laws of physics are not the same at all points in time) then energy can be created or destroyed [1]. So that would be quite a shocker. [1] https://en.m.wikipedia.org/wiki/Noether%27s_theorem

Doesn't dark energy do exactly that? 70% of the energy of the universe doesn't seem to want to play by our rules!
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