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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

#211

Post by severila »

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 be interested in "Unrewarded" by "Ben Moore" which has an interesting take by telling the history of astronomy through the lives of those that made these discoveries but were not awarded a Nobel Prize.

Re: Webb and Hubble confirm Universe's expansion rate

#212

Post by luc4sdreyer »

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…

> 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.wikipedia.org/wiki/Aristarchus_of_Samos#Distance_...

Nice video about the cosmic distance ladder by Terence Tao: https://www.youtube.com/watch?v=7ne0GArfeMs

Re: Webb and Hubble confirm Universe's expansion rate

#213

Post by denton-scratch »

orlp wrote: post #194
theoreticalmal wrote: post #141

Earlier quoted context omitted.

I can’t believe it. First they take Pluto from us, next they’re going to tell me the static on my tv set isn’t the remnants of the Big Bang, but just hot dust? My childhood is crumbling!

Your comment made me realize how some younger people have no idea of, or at least no first-hand experience of static on TV and radio since it is all digital nowadays.

See also https://en.wikipedia.org/wiki/White_Dot

Re: Webb and Hubble confirm Universe's expansion rate

#214

Post by zuzun »

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!

Big Bang: The Origin of the Universe by Simon Singh.

Re: Webb and Hubble confirm Universe's expansion rate

#215

Post by luc4sdreyer »

pfannkuchen wrote: post #210

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?

>from one point in space

- We have multiple observatories on and around the planet - The Earth is moving around the Sun - The Sun is moving around the centre of the galaxy - The galaxy is moving towards the great attractor, etc

The Copernican principle states that humans, on the Earth or in the Solar System, are not privileged observers of the universe, that observations from the Earth are representative of observations from the average position in the universe. This has been tested in various ways: https://en.wikipedia.org/wiki/Copernican_principle#Tests_of_...

A nice PBS spacetime video about the topic: https://www.youtube.com/watch?v=q-6oU3jXAho

You can also ask how do we know that the laws of physics haven't changed over time. We don't. But at some point you have to make a few basic assumptions in order to have any hope of making scientific progress.

Re: Webb and Hubble confirm Universe's expansion rate

#216

Post by brabel »

orlp wrote: post #194
theoreticalmal wrote: post #141

Earlier quoted context omitted.

I can’t believe it. First they take Pluto from us, next they’re going to tell me the static on my tv set isn’t the remnants of the Big Bang, but just hot dust? My childhood is crumbling!

Your comment made me realize how some younger people have no idea of, or at least no first-hand experience of static on TV and radio since it is all digital nowadays.

I have a super modern flatscreen. Sometimes, when it can't connect to the laptop it shows what I believe is "simulated" static noise! I love that :D

Re: Webb and Hubble confirm Universe's expansion rate

#217

Post by mr_mitm »

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?

Yes, the "drifting" component you speak of is called the peculiar velocity. It's responsible for the "finger of god" effect if we don't account for it (galaxies appear to be aligned along the line of sight of the observer) and becomes negligible at large enough distances. I guess technically it's hard to differentiate because it's usually random, but it enters the error analysis and is accounted for.

Re: Webb and Hubble confirm Universe's expansion rate

#218

Post by denton-scratch »

wavefunction wrote: post #84
explaininjs wrote: post #26

Earlier quoted context omitted.

> Of course, all the results have error bars. Not to mention the underlying philosophical assumptions, such that the "rate of time" has been constant across all of... time. Aka: How do we know a "year" 13 Billion "years" ago bears any resemblance to one now? What would it mean for it not to?

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.

Re: Webb and Hubble confirm Universe's expansion rate

#219

Post by risfriend »

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...

Re: Webb and Hubble confirm Universe's expansion rate

#220

Post by munksbeer »

EnterpriseTell wrote: post #126
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…

>In short, even if galaxies weren't accelerating -Galaxies are not accelerating, space is expanding. > Imagine there are some objects in space all moving in random directions and speeds, relative to Earth... -No, In your scenario then end result would be a most static average distance between all objects in the universe. As an infinite number of objects come from infinite distances, there would ALWAYS be objects in t…

What does "space is expanding" mean? That the distance between objects is increasing? How can you tell the difference between "space expanding" and "objects moving in a non-expanding space"? Is there any way to tell the difference or is it just that all objects are moving away at the exact speeds that satisfies the "space expanding" explanation and nothing else?

But then, I'm back to what does "space is expanding" mean? What is doing the expansion?

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