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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

#181

Post by russdill »

acyou wrote: post #81

Even though the title is copied from the article, we should change the title to "New data indicates the Webb and Hubble telescopes agree on the universe's expansion rate, but not with the cosmic microwave background measurement based expansion rate"

Even the article seems confusing at first. The new measurements don't seem to be shedding light on anything or removing any confusion. They just confirm that hubble measurements already made. The Hubble tension remains as confounding a problem as ever.

Re: Webb and Hubble confirm Universe's expansion rate

#182

Post by russdill »

sudom82 wrote: post #140

This article is titled "Webb and Hubble confirm Universe's expansion rate", however I don't see the expansion rate actually listed there, or in the comments. I see a mention of age, but not the rate. Does anyone know the rate? I clicked through to the paper itself[1], but wasn't able to interpret it from the details I could see [1]: https://iopscience.iop.org/article/10.3847/2041-8213/ad1ddd

It seems like a better title would be "Webb confirms Hubble's measurement of Universe's expansion rate"

Re: Webb and Hubble confirm Universe's expansion rate

#183

Post by rexer »

physicles wrote: post #169

The article mentions the cosmic distance ladder, which is one of my favorite things in all of science. How do we know how far away the really far stuff is? It's non-trivial and I find the history fascinating. It all started with knowing the distance from the earth to the sun. Nobody had a clue until Richer and Cassini got within 10% in 1672. Then we nailed it down in 1769 with James Cook's voyage to Tahiti, the prima…

Great comment! Maybe you can help me with a book recommendation?

I was recently looking for a book which was basically your comment, but more in depth and covered the last couple thousand years. I wanted a to read about the history of astronomy - yknow, what was the state of the art in, say, 1350 or whatever. If you know of anything, I’d be super interested!

Re: Webb and Hubble confirm Universe's expansion rate

#184

Post by superjan »

rf15 wrote: post #53
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…

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.

And don’t forget cosmic inflation.

Re: Webb and Hubble confirm Universe's expansion rate

#185

Post by hummingn3rd »

physicles wrote: post #169

The article mentions the cosmic distance ladder, which is one of my favorite things in all of science. How do we know how far away the really far stuff is? It's non-trivial and I find the history fascinating. It all started with knowing the distance from the earth to the sun. Nobody had a clue until Richer and Cassini got within 10% in 1672. Then we nailed it down in 1769 with James Cook's voyage to Tahiti, the prima…

If you speak French or don't mind translating, there is this great video that goes through these techniques in layman's terms https://www.youtube.com/watch?v=FGwmAEMabm4&t=1

Re: Webb and Hubble confirm Universe's expansion rate

#186

Post by the-mitr »

garrettgarcia wrote: post #162
narag wrote: post #105

Earlier quoted context omitted.

How do we know that galaxies are accelerating away from us and not moving at constant speed? There's a more basic question: How do we know the galaxies are moving? It seems (I haven't seen any other response, like... ever) that we have one and only one way to measure the speed of galaxies: the red shift. It's impossible to triangulate those huge distances and the time scale would also be a barrier, so no way of confi…

The American astronomer, Halton Arp, had a theory he called "intrinsic redshift". My limited understanding is that he saw evidence of "very close" and "very far away" structures that are connected to each other in space, which makes no sense. He theorized that redshift may also be indicative of the age of a galaxy, rather than only indicating velocity. The interpretation of redshift as velocity is also the primary re…

His book Seeing Red which raises several interesting and troublesome questions for the standard big bang model is worth a read.

Re: Webb and Hubble confirm Universe's expansion rate

#187

Post by semi-extrinsic »

Sprocklem wrote: post #168
k7sune wrote: post #132

Earlier quoted context omitted.

“Degrading” sounds very intuitive to me. Can the frequency of the light waves simply slow down over a very long distance/time? Or maybe the speed of light simply slows down over an unimaginably long distance? We don’t have any model to describe such behavior, but everyday objects around us all slow down one way or another, what makes light so different?

IIRC, this was one of the explanations proposed when the existence of a red shift was first noted: that the light is somehow slowly losing its energy over very long distances, becoming “redder” as it did so. It ultimately lost out to the dark energy / space-time expansion theory, although I do not recall why. Presumably there was some observation that precluded “degrading” light from being the sole explanation.

There are several challenges for "tired light", or indeed any theory that's an alternative to expansion of the universe.

The theory has to explain why the light gets redshifted, but does not get blurred, and the spectral lines do not get broadened. This severely restricts the type of interactions possible. Also the theory has to explain the consistency between redshifts within our own galaxy, to that of far-away galaxies.

Re: Webb and Hubble confirm Universe's expansion rate

#188

Post by Veserv »

hnfong wrote: post #176
Veserv wrote: post #68

Earlier quoted context omitted.

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

Saying "X is true because otherwise, it would be quite a shocker" isn't really a proof. It's almost an appeal to common sense. (which, admittedly, is often the best argument we have). IMHO there's often a bit of over-confidence among scientists about the universe being 13 billion years old and what happened during the Big Bang, if it just relies on such a common sense argument. I know it's unscientific to suggest may…

I did not present proof. They asked what it would mean and a consequence of physical laws not being time invariant would be that energy does not need to be conserved.

To the extent that relates to epistemology that would be more like anti-proof I guess? It does not prove that the laws are time invariant, rather it raises the bar to demonstrate that the laws are not time invariant because that means energy need not be conserved. You can not get one without the other without attacking even deeper fundamentals of modern scientific models. So you must either demonstrate the linked claims, which are pretty foundational themselves, or you must overturn basically everything; both of which demand very robust evidence.

Re: Webb and Hubble confirm Universe's expansion rate

#189

Post by suzzer99 »

daxfohl wrote: post #27
FredPret wrote: post #9

Unbelievable how much we can work out from just the odd photon hitting us from somewhere in the great unknown.

It's astounding to me that space is so empty that in the billions of light years from here to the edge of the universe, there's orders of magnitude less total interference than what you get from a small cloud. It's also astounding that celestial objects emit enough photons that thousands per second travel within the arc that goes the distance from the star to somewhere inside the radius of your pupil. And if this was…

Also that the light and gravitational waves from colliding neutron stars can travel 100 million light years and arrive at earth within a second of each other. That's a mind-bogglingly small amount of drag.

Re: Webb and Hubble confirm Universe's expansion rate

#190

Post by merek »

For those interested in the cosmic distance ladder, David Butler has an excellent youtube series "How far away is it?", detailing the methods used to estimate distance along the cosmic distance ladder, the history, and examples. I highly recommend.

https://www.youtube.com/playlist?list=PLpH1IDQEoE8QWWTnWG5cK...

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