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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

#341

Post by gitaarik »

Another interesting measurement discrepancy that scientists initially ascribed to measurement error is the Axis of Evil. The first space telescope Cosmic Background Explorer (COBE), launched in the 90's, that made a map the cosmic microwave background (CMB) included a pattern in it which aligns the CMB with the solar system's plane very precicely, which is hard to ascribe to chance. This contradicts the Copernican principle, which says that earth and the solar system is not special and any solar system and location in the universe is not special.

Scientists thought it must be something to do with the COBE telescope which caused this anomaly. They thought it would disappear with the next space telescope.

The second space telescope that measured the CMB, the Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001, made a more precise, higher resolution image of the CMB. However, the anomaly was still there. Still scientists thought there must be something wrong in the measurements or calculations. They were keeping their hopes up for the third space telescope that would measure the CMB.

The third space telescope, the Planck Surveyor, launched in 2009, made even more precise measurements. However, the anomaly still persists, and to this day. That is why the anomaly has gotten the name "Axis of Evil", because it defies all our understanding of the universe!

Re: Webb and Hubble confirm Universe's expansion rate

#342

Post by denton-scratch »

explaininjs wrote: post #320
denton-scratch wrote: post #303

Earlier quoted context omitted.

> whether there exists an external "system clock" I'll ignore your analogy with a CPU, which I don't think is apposite. Whether there's a 'system clock', a sort of reference clock that can tell you how fast time is passing, so you can calibrate other clocks against it, seems to be the same category error. As far as I can see, either time is all there, all at once; or one second lasts exactly one second. (I've perpetr…

You're certainly welcome to completely ignore the question at hand, it's just surprising that you'd use so many characters to do so. The question is if there's a different sort of thing beyond our idea of time. We have our concept of N caesium oscillations is the base reference for everything, and the duration of all action is derived from it. Could there be more depth to the rate at which things occur than that, esp…

> You're certainly welcome to completely ignore the question at hand

What I ignored was an analogy. Not an argument from analogy; and not a question. Just a rhetorical device, which I considered irrelevant, and didn't feel like arguing about.

> the base reference for everything

Caesium oscillations are a proxy for the passage of time. I can imagine a universe in which the rate of Caesium oscillations might vary, or be influenced, making atomic clocks unreliable. I don't know how one might measure the passage of time directly; I suspect it's impossible, and can only be done with proxies.

I don't see why you couldn't have more than one timescale operating and interacting. It's an interesting speculation. But William of Ockham advised against multiplying hypotheses; and I can't see what multiple interacting timescales might explain, that can't be explained without them.

Re: Webb and Hubble confirm Universe's expansion rate

#343

Post by diedyesterday »

Kerbonut wrote: post #155
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?

Of course the rate of expansion is not constant; That's the whole deal with dark energy which is understood to drive accelerated expansion of space due to its negative pressure (when you make something with negative pressure larger in volume you have to do positive work on it or give it energy and that energy is dark energy).

But the Hubble tension is something else: It's about measurements of H0 (the current value of the Hubble parameter) using two different methods (early universe and CMB OR recent universe and supernovae, etc.) that do not agree. The disagreement is about two estimations of the current rate of expansion called H0; Everyone agrees H(t) has been increasing (=accelerating expansion); But accelerating toward which recession velocity is the question.

Re: Webb and Hubble confirm Universe's expansion rate

#344

Post by thehappypm »

semi-extrinsic wrote: post #187
Sprocklem wrote: post #168

Earlier quoted context omitted.

IIRC, this was one of the explanations proposed when the existence of a red shift was first noted: that the light is somehow slowly losing its energy over very long distances, becoming “redder” as it did so. It ultimately lost out to the dark energy / space-time expansion theory, although I do not recall why. Presumably there was some observation that precluded “degrading” light from being the sole explanation.

There are several challenges for "tired light", or indeed any theory that's an alternative to expansion of the universe. The theory has to explain why the light gets redshifted, but does not get blurred, and the spectral lines do not get broadened. This severely restricts the type of interactions possible. Also the theory has to explain the consistency between redshifts within our own galaxy, to that of far-away gala…

Tired light is tricky to be possible because light doesn’t experience time or distance since it travels at c. Light itself from its frame of reference is emitted and received simultaneously. That’s not to say other perspectives can have different views though!

Re: Webb and Hubble confirm Universe's expansion rate

#345

Post by thehappypm »

__turbobrew__ wrote: post #163
narag wrote: post #105

Earlier quoted context omitted.

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…

Degrading light sounds like an interesting idea to me, you could call it the “cosmological damper” if you will. Thought experiment: imagine you have light particles in a perfectly circular orbit around a black hole. Does the light ever fall into the black hole or does it orbit for eternity?

Can photons collide? My understanding is they can’t.

If they could, Hawking radiation would interfere with the eternal orbit.

Re: Webb and Hubble confirm Universe's expansion rate

#346

Post by thehappypm »

munksbeer wrote: post #297
tvshtr wrote: post #264

Earlier quoted context omitted.

Imagine a deflated baloon with two dots drawn close to each other. Now inflate it; the dots didn't move but the plane that they were drawn/positioned on did.

I understand that concept. I'm asking, how can you materially tell the difference?

Nobody can answer because nobody knows

Re: Webb and Hubble confirm Universe's expansion rate

#347

Post by thehappypm »

gitaarik wrote: post #341

Another interesting measurement discrepancy that scientists initially ascribed to measurement error is the Axis of Evil. The first space telescope Cosmic Background Explorer (COBE), launched in the 90's, that made a map the cosmic microwave background (CMB) included a pattern in it which aligns the CMB with the solar system's plane very precicely, which is hard to ascribe to chance. This contradicts the Copernican pr…

Fascinating! The flat earthers may be wrong about the Earth, but maybe the universe is rather flat!

Re: Webb and Hubble confirm Universe's expansion rate

#348

Post by sapiogram »

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.

His method was fundamentally sound though. He realized that moonlight is reflected sunlight, and that if you observe the angle between the sun and the moon in the sky at exactly half moon, you can calculate the distance to the sun relative to the distance to the moon.

Re: Webb and Hubble confirm Universe's expansion rate

#349

Post by naasking »

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…

> Some sort of error in how we measure the variations in the CMB.

IIRC, the prediction that comes from the CMB depends on the lambda cold dark matter model, and there are plenty of independent reasons to be skeptical of that model already. If I were betting which one's most likely to be wrong, that's where I'd put my money.

Re: Webb and Hubble confirm Universe's expansion rate

#350

Post by ubutler »

Cthulhu_ wrote: post #304
whimsicalism wrote: post #235

Earlier quoted context omitted.

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.

I appreciate that he worked on it at least. Around the same era, someone else calculated the circumference of the earth (and that it was round) in a pretty accurate fashion (between −2.4% and +0.8% off) based on measuring shadows on equally sized posts at different locations on the same date. Googled, it was Eratosthenes, the cities were Alexandria and Syene/Assuan.

One of my favourite episodes of Cosmos centres around Eratosthenes’ calculation of the circumference of the Earth: https://youtu.be/G8cbIWMv0rI?si=CuX49ki1GIvBLpeL
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