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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

#271

Post by nolta »

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!

You might like "Coming of Age in the Milky Way".

Re: Webb and Hubble confirm Universe's expansion rate

#272

Post by sophacles »

hnfong wrote: post #174
sophacles wrote: post #152

Earlier quoted context omitted.

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…

People can be right about problems with a process or way of thinking without being the next Einstein. There's no need to get personal.

But in this case you and your friend are not right about the process. There was a claim that "the models aren't being updated based on the new data" which is categorically false. It's not that they pointed out problems in the process, it's that they flat out lied about things - such dishonesty doesn't help solve any problems you imagine you see, its just trolling.

Re: Webb and Hubble confirm Universe's expansion rate

#273

Post by mrguyorama »

explaininjs wrote: post #247
baq wrote: post #206

Earlier quoted context omitted.

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

It's really not. If there is nonzero energy, and our current models don't allow for energy to be created, either we need new models that do allow for energy to be created (time-variant physics, for instance), or we need the existing models to propose a way it was initialized. Without that there's a gaping hole in the model the size of all of the energy in the universe. Certainly you can't 1) have a model where energy…

>or we need the existing models to propose a way it was initialized.

We have that, it's the big bang.

Re: Webb and Hubble confirm Universe's expansion rate

#274

Post by effingwewt »

munksbeer wrote: post #251
baq wrote: post #233

Earlier quoted context omitted.

space expanding means what it literally says: there is more space everywhere at once. there was less a moment ago and now there's more. the longer the distance, the more space gets added in between, thus the effect is extreme on universe scale and undetectable on planetary scales.

Well yes, but did you read my post in detail? I asked what the difference was between "space expanding" vs "objects moving away from each other". And secondly, what is the mechanism for "space expanding"? What is "space" in this context? What actually is expanding?

Let me try to explain- galaxies moving would be like balls floating in a pool. The galaxies are moving across the water.

Space moving would be like balls placed on a bed sheet and the sheet expanding. The galaxies aren't moving- the sheet is.

What's actually happening is more like galaxies moving around on a sheet that's being pulled further at all sides.

Re: Webb and Hubble confirm Universe's expansion rate

#275

Post by cbolton »

arbitrage wrote: post #93
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.

Take a star in a region of the universe that recedes from us at 3c. In what sense is the star not traveling faster than the speed of light relative to us?

Re: Webb and Hubble confirm Universe's expansion rate

#276

Post by explaininjs »

mrguyorama wrote: post #273
explaininjs wrote: post #247

Earlier quoted context omitted.

It's really not. If there is nonzero energy, and our current models don't allow for energy to be created, either we need new models that do allow for energy to be created (time-variant physics, for instance), or we need the existing models to propose a way it was initialized. Without that there's a gaping hole in the model the size of all of the energy in the universe. Certainly you can't 1) have a model where energy…

>or we need the existing models to propose a way it was initialized. We have that, it's the big bang.

How remarkably unsatisfactory.

The argument being:

You can't propose physics ever changed, that'd mean energy could have been created at some point!

Energy was created at some point, wouldn't it be nice to know when?

Everything created at the Big Bang exactly as it is now, stop asking questions.

Re: Webb and Hubble confirm Universe's expansion rate

#277

Post by explaininjs »

denton-scratch wrote: post #218
wavefunction wrote: post #84

Earlier quoted context omitted.

I have had the same thought that primordial reality had the same timestream as us but it was much longer, like the first "year" of reality was far longer than one year today, just the thinking "could time have been shorter or longer, why not"

> the first "year" of reality was far longer than one year today This talk about the "rate of time" doesn't make any sense to me. A second takes one second, and always has. Isn't this like asking whether the length of a metre might have changed over time? Or the mass of a kilogramme? It looks to me like a category error.

`This talk about the "rate of execution" doesn't make any sense to me. A cycle takes one cycle, and always has.`

The root of the question is whether there exists an external "system clock", and what that would even mean.

Re: Webb and Hubble confirm Universe's expansion rate

#278

Post by explaininjs »

jMyles wrote: post #177
explaininjs wrote: post #170

Earlier quoted context omitted.

Yes, an external reference clock is needed. If a computer chugs along doing { counter++; } at 1 clock cycle per clock cycle for 13.7 billion clock cycles, it will think 13.7 billion clock cycles have passed when counter is 13.7 billion. On the other hand, if a computer chugs along at one clock cycle per clock cycle for 1 clock cycle, and reads &counter and sees 13.7 billion, it will think 13.7 billion clock cycles ha…

I agree with you 100% on your assessment of what can be known, but I think I disagree nearly as strongly on your assessment of the humanity that springs from attempting to know it. To exist in the state you describe - with neither start state nor isolation level measurable in any tamper-proof way - and to yet still dedicate one's life to observing and pondering the complexity of the resulting cosmos is, to my eye, la…

I think the hubris comes in when folks assume that because that answer is presented by Science/Observation rather than Religion/Philosophy, it's somehow guaranteed to be "more accurate", when in reality both are guesses with equally unknowable error bars.

Re: Webb and Hubble confirm Universe's expansion rate

#279

Post by raattgift »

sanxiyn wrote: post #242
tails4e wrote: post #203

Earlier quoted context omitted.

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.

Error analysis of cosmic distance ladder is fiercely technical subject. https://arxiv.org/abs/1103.2976 Table 5 is titled "H0 Error Budget for Cepheid and SN Ia Distance Ladders". (It is old and the field is moving fast, but this is what I happened to remember.) Among total error of 3.1%, Cepheid reddening is 1.4% and the second largest source of uncertainty. SN Ia statistics is the largest with 1.9%. Rarely discusse…

> Rarely discussed in popular treatment is anchor distance

Yes, and I'm sad that it's so rare.

The Megamaser Cosmology Project is incredibly awesome; combining line of sight acceleration, velocity, velocity gradient, and observer angle on the sky is very "anchor".

https://safe.nrao.edu/wiki/bin/view/Main/MegamaserCosmologyP...

Gaia seems to be making good progress on direct parallax up to kiloparsecs.

And always happy to plug ASAS-SN https://www.astronomy.ohio-state.edu/asassn/index.shtml> (The deleted @SuperASASSN was one of the best astro follows on twitter some years ago), who have found an awful lot of detached eclipsing binaries: https://academic.oup.com/mnras/article/517/2/2190/6695108?lo...>.

Re: Webb and Hubble confirm Universe's expansion rate

#280

Post by mrguyorama »

pigpang wrote: post #197
a_random_canuck wrote: post #145

Earlier quoted context omitted.

> do we account for velocity in determining whether light traveling at c towards earth will ever reach us? No, because the speed of light is constant for all observers. From our frame of reference on earth, light from distant receding galaxies is always moving towards us at exactly the speed of light, c. Those galaxies also observe the light moving away from them at exactly c. That seems contradictory and unintuitive…

> That seems contradictory and unintuitive, that two observers moving away from each other both measure light moving c relative to themselves, but that’s reality. Light is a wave. Photon is a complex thing (Hopfion?), but it's a wave, so it waves something, a medium. Speed of wave propagation in a medium is constant. IMHO, it's intuitive.

>but it's a wave, so it waves something, a medium.

Which was unobserved in the michleson-morely experiment and other followup experiments because....?

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