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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

#241

Post by dexterdog »

whimsicalism wrote: post #235
luc4sdreyer wrote: post #212

Earlier quoted context omitted.

> Nobody had a clue In the 3rd century BC, Aristarchus calculated that the Sun was between 18 and 20 times farther away from the Earth than the Moon, and proposed the Heliocentric model as a result. The true value is instead approximately 400 times. But it's incredible given that he didn't have lenses, the value of Pi, and that the Geocentric model was considered correct until 1800 years after his death. https://en.w…

yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”. He didn’t say nobody had a clue about heliocentrism.

But I believe he was the winner for many years under price is right rules.

Re: Webb and Hubble confirm Universe's expansion rate

#242

Post by sanxiyn »

tails4e wrote: post #203
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.

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 discussed in popular treatment is anchor distance, the third largest source with 1.3%. It is uncertainty of bottom lungs of the ladder, eg the distance to Large Magellanic Cloud before Cepheid and SN Ia are involved.

Re: Webb and Hubble confirm Universe's expansion rate

#243

Post by jug »

I can recommend Dr. Becky's introduction to the issues surrounding the Hubble Tension and recent JWST measurements in this 16 minute clip, as she introduces laymen to the problems well: https://www.youtube.com/watch?v=hps-HfpL1vc

It's an older clip, but it checks out... ;) (still JWST discoveries and she most importantly introduces the viewer to the still remaining conflicts)

Re: Webb and Hubble confirm Universe's expansion rate

#244

Post by HarVard93 »

tails4e wrote: post #201
rexer wrote: post #183

Earlier quoted context omitted.

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

ya

Re: Webb and Hubble confirm Universe's expansion rate

#246

Post by cwmma »

whimsicalism wrote: post #235
luc4sdreyer wrote: post #212

Earlier quoted context omitted.

> Nobody had a clue In the 3rd century BC, Aristarchus calculated that the Sun was between 18 and 20 times farther away from the Earth than the Moon, and proposed the Heliocentric model as a result. The true value is instead approximately 400 times. But it's incredible given that he didn't have lenses, the value of Pi, and that the Geocentric model was considered correct until 1800 years after his death. https://en.w…

yeah i would call estimating it as 20x when it is actually 400x firmly within “not having a clue”. He didn’t say nobody had a clue about heliocentrism.

Plus they didn't know the distance to the moon

Re: Webb and Hubble confirm Universe's expansion rate

#247

Post by explaininjs »

baq wrote: post #206
explaininjs wrote: post #116

Earlier quoted context omitted.

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'.

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 is constant 2) believe there is nonzero energy in the universe and 3) dismiss any model where energy can change as bogus out of hand because you believe it should be constant, without counter-proposing how it even got here.

Re: Webb and Hubble confirm Universe's expansion rate

#248

Post by dmd »

root_axis wrote: post #159
dmd wrote: post #133

Earlier quoted context omitted.

[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.

How does what they said differ from simply saying the universe is expanding - but in a word-salady way that obfuscates it?

Re: Webb and Hubble confirm Universe's expansion rate

#249

Post by QuadmasterXLII »

risfriend wrote: post #219
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…

The distance was also known in 16th century as per Hindu hymn of hanuman chalisa - https://hinduism.stackexchange.com/questions/10370/did-our-a...

I'm sure your goal is to boost the intellectual reputation of ancient hindu philosophy, but you're mostly scuffing the intellectual reputation of hinduism.stackexchange.com

Re: Webb and Hubble confirm Universe's expansion rate

#250

Post by sebzim4500 »

throwawaymaths wrote: post #104
sebzim4500 wrote: post #92

Earlier quoted context omitted.

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

> According to the standard big bang theory the CMB should look like black body radiation.

Yes, that's my point.

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

Surely that can only be true for a very specific distribution of temperatures? To go to an extreme, if you combine the spectrum of two objects of different temperatures you do not get anything like a black body curve.

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