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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

#151

Post by vlovich123 »

itishappy wrote: post #107
vlovich123 wrote: post #71

Earlier quoted context omitted.

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!

The inflationary epoch where it expanded by 10^78 in volume happened in the first 10^-32 seconds. The furthest galaxy we can see (fairly poorly) is 300M years after the Big Bang. It's likely if time or the rules were different, 300M years was enough for things to mostly die down to steady state. And as you say, they match more or less but those errors could easily hide remnants of when things were different. Of course, these are all numbers that assume the Big Bang theory is correct which is difficult to impossible to falsify since we can't possibly observe or test anything from that long ago. We'll have to wait to see if refinements to our model that clear up contradictions change what we think about the beginning of the universe and other boundary conditions.

Re: Webb and Hubble confirm Universe's expansion rate

#152

Post by sophacles »

willis936 wrote: post #129
pdonis wrote: post #122

Earlier quoted context omitted.

I'm not sure what you mean by "phantoms in the data". The distribution of stress-energy is a free parameter in GR; it has to be inferred from observations. The terms "dark matter" and "dark energy" are just names for, respectively, "stress-energy that acts like the matter we can see, but we can't see it", and "stress-energy that acts like a cosmological constant". Neither of those things poses any problem for GR, sin…

>"Dark matter" poses a problem for particle physicists, who have so far been unable to find any fundamental particles that would produce the observed properties. It's clear to me why we haven't made any new discoveries in cosmology in the past two decades. It's this exact attitude of "the model is the truth". All models are wrong. The data can help you improve it, but you have to at least want to improve it.

What do you think they do now?

How do you propose they do it differently?

What evidence do you have that what they are doing now doesn't work, and does the all the evidence of how they work support your hypothesis?

Be detailed, because your comment just has some motivational speaker nonsense but no depth. For example, in the last 20 years cosmology has:

+ Refined its model of stellar formation based on observational data of the number of planets found observationally, and used this to validate and invalidate several model adjustments.

+ Observed galaxies that appear not to have dark matter, and by their existence and behavior validate some theories of dark matter, and validated others, which predict such galactic behavior. (e.g. some theories attempting to update gravity).

+ Run simulations of stellar and glactic formation that predicted structures in the universe that were later observed.

Everywhere they look they are finding things the models don't explain well, and refining the models - that is literally using the data to improve the models.

If you think you can come up with something better, then do it - all you gotta do is make up some mumbo jumbo and write down any old equation. It probably should:

- provide the same results as were observed when the plugging in the experimental parameters of existing experiments.

- explain "wierd stuff" in the data that existing models couldn't.

- predict future observations of the known phenomena with the same or better accuracy as the old model

- predict currently unobserved and unpredicted phenomena

Go ahead and take a stab real quick - I'm sure you can do it. I mean Gallieo did it, so did Newton and Einstein. Next up is willis936.

Re: Webb and Hubble confirm Universe's expansion rate

#153

Post by javajosh »

narag wrote: post #105
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 confi…

>It's impossible to triangulate those huge distances

Galaxies are BIG. Andromeda is faint, but the same angular size as the moon. It's 2.5Mly away, but it's also 150kly across. Over a long enough time line you could do triangulation on it. In fact it's moving toward our galaxy, but very, very slowly compared with its diameter at 110kps. But yeah, in theory you could do triangulation on it over a very long period of time.

Re: Webb and Hubble confirm Universe's expansion rate

#154

Post by antod »

mjfl wrote: post #146
digging wrote: post #127

Earlier quoted context omitted.

Without being able to harvest dark energy, it's actually the exact opposite.

The extra energy comes from the increase in gravitational potential energy between objects. The accelerating increase in this potential energy implies the total energy of the universe is increasing. I’m not talking about harvesting dark energy directly.

I'm no physicist, but isn't the gravitational potential energy between two objects inversely proportional to the distance between them?

Re: Webb and Hubble confirm Universe's expansion rate

#155

Post by Kerbonut »

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 the rate of expansion is not constant?

Re: Webb and Hubble confirm Universe's expansion rate

#156

Post by mjfl »

antod wrote: post #154
mjfl wrote: post #146

Earlier quoted context omitted.

The extra energy comes from the increase in gravitational potential energy between objects. The accelerating increase in this potential energy implies the total energy of the universe is increasing. I’m not talking about harvesting dark energy directly.

I'm no physicist, but isn't the gravitational potential energy between two objects inversely proportional to the distance between them?

it is, in the negative direction though. So increasing the distance increases the potential energy by making -1/r closer to zero.

Re: Webb and Hubble confirm Universe's expansion rate

#157

Post by dvsfish »

dmd wrote: post #133
xeonmc wrote: post #128

Earlier quoted context omitted.

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…

[flagged]

While its probably totally wrong, I think your tone and general attitude to people throwing around imaginative and creative ideas is extremely unproductive and frankly rude. If you want to stifle creative discussions, this is exactly how you'd do it. I found the post to be very stimulating regardless of its validity. And it's not like they're trying to spread it as gospel. There was a lot of disclaimer.

Re: Webb and Hubble confirm Universe's expansion rate

#158

Post by undersuit »

puzzledobserver wrote: post #149
digging wrote: post #127

Earlier quoted context omitted.

Without being able to harvest dark energy, it's actually the exact opposite.

What would a hypothetical dark energy engine look like?

It would harness dark energy. /s

We haven't detected dark matter or dark energy outside of their visible effects on the larger universe. Maybe we can't interact with it with baryonic matter. A dark energy engine made out of dark matter would be invisible.

Re: Webb and Hubble confirm Universe's expansion rate

#159

Post by root_axis »

dmd wrote: post #133
xeonmc wrote: post #128

Earlier quoted context omitted.

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…

[flagged]

I think if you're going to dismiss the comment in such a flippant and condescending manner you should at least explain what's wrong with it.

Re: Webb and Hubble confirm Universe's expansion rate

#160

Post by arandomusername »

lagrange77 wrote: post #109
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?

I think we observed some of the galaxies moving away from us at rates faster than speed of light, multiple times faster, which wouldn't work with objects drifting away if we hold by that speed of light is max speed matter can move at.
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