Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Webb and Hubble confirm Universe's expansion rate

esa.int

Post reply on HN
Print view View original

101–110 of 380 posts

Re: Webb and Hubble confirm Universe's expansion rate

#101

Post by rhelz »

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

For real? That is a very interesting observation.

Re: Webb and Hubble confirm Universe's expansion rate

#102

Post by colechristensen »

NemoNobody wrote: post #80
colechristensen wrote: post #69

Earlier quoted context omitted.

If your idea was the case there would always be new things from very far away heading towards us, this is not the case. If the universe is flat and infinite there would be no end in supply of new galaxies with all velocities and you would always have the same mix as the initial mix of velocities. That’s not what we see.

I'm so glad "the infinite universe" as an idea is finally falling off. It works great in the Hitchhikers Guide, I love the floopy mattresses and planets that grow screwdrivers but nothing real is infinite. I didn't even realize how many people held that belief til that article about how the universe isn't as big as we thought

Huh? Every evidence points to a flat infinite universe. Nothing but speculation points to anything otherwise.

Re: Webb and Hubble confirm Universe's expansion rate

#103

Post by ijustlovemath »

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…

One thing that is not often mentioned is that this effect only applies outside the local supergroup; within the supergroup gravity overrides the expansion of spacetime and holds us together (for now!)

Re: Webb and Hubble confirm Universe's expansion rate

#104

Post by throwawaymaths »

sebzim4500 wrote: post #92
throwawaymaths wrote: post #85

Earlier quoted context omitted.

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?

No. According to the standard big bang theory the CMB should look like black body radiation.

As for smearing, IIRC black body curve has the central limit property

Re: Webb and Hubble confirm Universe's expansion rate

#105

Post by narag »

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?

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 confirming the red shift calculations with a different method. That means that if the red shift was caused by any other effect, say the light "degrading" after millions of years of travelling the void, all the calculations would be invalid.

I've asked about this many times and the answers are in the line of "we don't know any other reason for the light to red shift" and "the current theoretical frame is consistent", even if there isn't any other measure to be consistent with.

There was a prediction (expansion is related to Big Bang) that the far away galaxies, being younger, would have a different composition. This prediction seems to be failing, but advances in instrumental could give us a more precise answer in the future.

Re: Webb and Hubble confirm Universe's expansion rate

#107

Post by itishappy »

vlovich123 wrote: post #71
dwattttt wrote: post #49

Earlier quoted context omitted.

How do we know ? Observations we can make plus models that relate those to the things we can't observe directly.

Unfortunately we can’t observe fundamental things like “what are the rules of physics and time at the beginning of the universe?”. We look for clues and make large assumptions, but given that the universe experienced a 10^78 factor expansion during the Big Bang, assuming that actually happened, then why would it make sense to assume that the rules of the universe today are the rules for the very early beginning of th…

Entirely reasonable assumptions! Our models match surprisingly well though... The CMB has a blackbody spectrum that aligns with predictions, we see galaxies more or less when and where we'd expect them, stellar populations look like what we'd expect for a universe made of hot hydrogen, and more! It's not quite perfect, but modern physics explains stuff really quite well even billions of years ago!

Re: Webb and Hubble confirm Universe's expansion rate

#109

Post by lagrange77 »

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…

Interesting, thanks!

Out of curiosity: Can we actually differentiate between the expansion of space itself and the drifting of objects within it in the same direction?

Post reply on HN