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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

#201

Post by tails4e »

rexer wrote: post #183
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!

Terence Tao did a great lecture on this, https://youtu.be/kY1gfrhNUIg?si=9u9k8of6-jRybwCG

Re: Webb and Hubble confirm Universe's expansion rate

#202

Post by pmayrgundter »

ta8645 wrote: post #147

Don't know why, but I recently got this gentleman's channel in my feed, who believes that there is no expansion at all: https://youtu.be/TGpjGVNVYEg?t=397 It's beyond my depth to explain why he's wrong.

Alexander Unziker. Also Eric Lerner, Pierre Robitaille

Re: Webb and Hubble confirm Universe's expansion rate

#203

Post by tails4e »

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…

I've often thought about this myself. I'm sure scientists involved are aware of the compounding errors with each step and build that in, but I'd love to see an analysis that breaks that down. When I first saw it I thought the errors due to cephids must be a large component of uncertainty, but really I've no idea how well contained that is.

Re: Webb and Hubble confirm Universe's expansion rate

#204

Post by jabits »

xeonmc wrote: post #128
dmd wrote: post #115

Earlier quoted context omitted.

You would have to come up with an explanation for such drifting to be occurring across the entire visible universe in precisely the same way, across billions and billions of light years.

Just a fringe speculation without any physical basis: maybe the Big Bang emits a 4-dimensional spherical shell of matter at c ? With the direction in which we are traveling at c called “time”, and the other three which we're not moving through called “space”; diverging rays having spatial velocity relative to each other equal to tan(alpha) i.e. flat projection; and at any given point on the 4-sphere's 3D surface ever…

This is a really interesting thought. I will be noodling on this tonight. Thanks

Re: Webb and Hubble confirm Universe's expansion rate

#206

Post by baq »

explaininjs wrote: post #116
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

Do you think the current amount of energy in the universe is 0? If not, how was it created?

That's a completely different question, to which the answer is 'we don't know'.

Re: Webb and Hubble confirm Universe's expansion rate

#207

Post by pigpang »

lp4vn wrote: post #150
pdonis wrote: post #113

Earlier quoted context omitted.

> I'm picturing more of an explosion in empty space. No, that's not what the big bang is. > this would imply a "center" to the explosion, which I've also heard is not the case That's correct. The big bang does not work like anything ordinary that you are used to imagining. The math is straightforward and unambiguous, but there is no good ordinary language description that corresponds to the math.

As I understand it, before the big bang the whole observable universe was contained in a small sphere and then it started to expand metrically. Is this interpretation correct? Another thing: suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? To an infinite void? Is it correct to say that stars radiate energy to the infinite…

It's just an interpretation. Your interpretation is similar to the Big Bang model of visible Universe expansion. If you can convince us that your model is better than other models, then we will use your model, but nobody can prove than a model is correct, unless we will find a hidden recorder somewhere which was turned on for few dozens of billion years.

Photon will hit something, or will travel until it will be redshifted to obvilion, or will travel until end of the medium (photon is a wave, so it waves something).

Re: Webb and Hubble confirm Universe's expansion rate

#208

Post by pigpang »

semi-extrinsic wrote: post #187
Sprocklem wrote: post #168

Earlier quoted context omitted.

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 gala…

My theory is that redshifting caused by gravitational background noise. I did calculation somewhere on HN or Youtube few months ago and numbers are of same magnitude.

Re: Webb and Hubble confirm Universe's expansion rate

#209

Post by scotty79 »

xeonmc wrote: post #82
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…

Could it be that nearby galaxies are akin to small angle approximations in spacetime trajectory, but as you get really far away (e.g. CMB) the perspective distortion increases hyperbolically? I notice that if you normalize the Hubble data by their Lorentz factor you get back a constant expansion rate: https://www.desmos.com/calculator/llhnja1ocb

Probably accidental?

Redshifts can be way higher than 1 that in your scaling is a magic value.

https://en.wikipedia.org/wiki/List_of_the_most_distant_astro...

Re: Webb and Hubble confirm Universe's expansion rate

#210

Post by pfannkuchen »

I don’t really understand how we can make conclusions about the entire universe when literally all of the data is collecting from one point in space. Couldn’t there be local effects that obfuscate global behavior?

Is there an implicit caveat asterisk on all such statements that is like “as far as we can possibly tell from the data we have” and the reality is we really, really don’t know for sure?

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