I've always thought as a layman that the weakest link in all of this is our cosmic distance ladder, seems like the most likely place that errors would stack up and lead us to some wrong conclusions. So may places for things to go wrong, we make a lot of assumptions about type 1a supernovas actually being a constant brightness, dust obscuring our view of them, plus all of the assumptions we've made about even measuring the distance between the ones we've measured. And its not like cosmologists havent acknowledged this, but I think a lot of the hubble tension might be solved once we figure out how to measure these distances more accurately.
The various candles are not independent yardsticks, nor are they just assumed to be true. Wherever possible they are compared against each other. And there are people who spend entire careers debating how dust absorbs light in order to best compensate for such things.
If measurements point to some sort of incongruity, questioning the accuracy of one's ruler is a fools trap. Altering the rulers to remove incongruities results in a spiral of compromises, internal debates that don't result in progress. If one suspects that the rulers are wrong, the answer is to build a better ruler. Not to arbitrarily chop bits off until the difficult observations go away.
I totally agree, hope my comment didnt come off to the contrary. As a layman, I consume most of my information through popsci sources (though I try to go more for the Dr. Beckys than the meatless or sensational stuff), and its generally described as something that we just take for granted - "we just found the oldest galaxy ever observed, only a few hundred million years after the big bang - and its too bright and has way more 'metals' than expected" - but we measured that with redshift, which makes a bunch of assumptions that of course they cant talk about in every video, but we dont talk about anyone questioning them.
I have no doubt that there are great scientist spending their entire careers trying to improve these rulers and measurements, but I also know that there are great scientists spending their entire careers basing everything on the best rulers they have...
> Freedman's latest calculation, which incorporates data from both the Hubble Telescope and the James Webb Space Telescope, finds a value of 70.4 kilometers per second per megaparsec, plus or minus 3%.
> That brings her value into statistical agreement with recent measurements from the cosmic microwave background, which is 67.4, plus or minus 0.7%.
Does it? As a lay person who can do basic arithmetic, this seems incorrect? Maybe there is some rounding or truncation, since I didn't check the source paper, or maybe I don't understand how confidence intervals work.
> These numbers are certainly close, but to my naive interpretation, the ranges don't overlap?
As is typical, the tolerances given are sigma values for an assumed normal distribution, not the width of a uniform distribution. The disagreement is less than five sigma, so (in the domain of physics) the disagreement is not considered significant enough to be a high-confidence indicator of new physics.
This wins some kind of award for most useful information packed into two sentences on HN. This is exactly what I've been wondering since this came out.
This is a big source of confusion when it comes to errors. I think most people think intuitively in terms of a 'peak-to-peak' specification of errors, i.e. range of X means that all possible values are within that range. But that's not really how statisticians think, and they tend to think in terms of standard deviation. Even if you soften the 'intuitive' view to 95% confidence range, that's about a 6x difference in terms of what the number means (assuming, optimistically, a gaussian distribution).
For a null hypothesis of “their differences are consistent with zero”, the p-value is 17%, equivalent to a 1.4 sigma difference. That’s pretty far from a reasonable rejection criterion for the null hypothesis. I think most people would agree that that means these measurements are plausibly consistent.
Nothing about this is obvious. The age of the universe is related to the integral over the inverse Hubble parameter. The age of the universe is founded by measuring the Hubble constant among other things, not the other way round.
> "Using its infrared detectors, we can see through dust that has historically plagued accurate measurement of distances, and we can measure with much greater accuracy the brightnesses of stars," added co-author Barry Madore, of the Carnegie Institution for Science.
It's amazing just rich the electromagnetic spectrum is for analyzing the universe, from radio to X-rays, and how complementary the pictures are. Though we get visually pleasing pictures in the visible spectrum, most of the really intellectually pleasing stuff of the past century has been outside the visible range.
Having waited half my life to see Webb finally launch, it's amazing to see how much we're discovering through it. Seems like every other day there's another insight found.
I have a total n00b question. Why would this be a “constant”? Wouldn’t different galaxies and different matter in the universe expand at different rates, and be an acceleration/deceleration, where one observation is the derivative or velocity of that one entity being observed?
A natural follow-up to your question might be: "If everything is expanding, then wouldn't the ruler itself be expanding, so the expansion becomes unobservable?"
I'm not a physicist, but from my understanding, the situation is a bit more complicated than the phrasing in your question suggests.
Observation #1: The light from far-away galaxies is redshifted (spectral lines are a bit off from where we'd expect them to be). This suggests that these galaxies are moving away from us. The farther away the galaxy, the more it is redshifted. This suggests that the farther away the galaxy, the faster it is moving. Observations indicate that the recession speed is directly proportional to distance.
This observation is consistent with general relativity, which suggests an expanding universe with homogeneous mass.
But on a smaller scale, gravitational binding somehow takes over, and on even smaller scale, things like electromagnetic and nuclear interactions start having a greater impact, and that's why the Milky Way isn't itself expanding. For that matter, even Andromeda (0.8 Mpc) is too close to be affected by Hubble-style expansion, which only becomes observable at the multi-megaparsec scale.
Hubble found that the recessional velocity of a galaxy is proportional to its distance. The proportionality constant is called the Hubble constant.
It's a bit of a misnomer though, because it's only constant through space, not time. At the time of discovery it was assumed to be constant in time, too.
The irony of course being that Hubble's original data is, at least in modern scientific analysis, very well compatible with "no expansion". There is _a lot_ of community flavour involved in how we talk about measurement results
Dumb question: why did we need to see far-away galaxys moving away faster than near galaxies to conclude that the universe was expanding? Wouldn’t just the fact that everything is moving away from us lead to the same conclusion?
> why did we need to see far-away galaxys moving away faster than near galaxies to conclude that the universe was expanding? Wouldn’t just the fact that everything is moving away from us lead to the same conclusion?
Imagine inflating a balloon onto which you've painted dots. All the dots move apart. But the ones furthest apart move apart faster than those close together. This is how you know the dots aren't just moving in their local environment, the entire space is expanding (everywhere).
(If you want a 1D representation, move your fingers apart at a constant rate. Consider how much further apart your pinky and index finger are compared with your middle and ring finger. That wouldn't happen if you just make a Spock hand.)
If we see farther away galaxies moving away at the same speed as nearby galaxies that means that all the expansion of the universe happens between us and the nearby galaxies (since the farther away galaxies wouldn't be moving away from the nearby galaxies). So we would have some kind of local expansion of space around our galaxy. This is if we see a redshift in all directions, if we see a redshift in one direction and a blueshift in the opposite direction, that just means that our galaxy is moving relative to the observed galaxies (also, such a dipole can be seen in the microwave background).
That is not a fact; there are stars that are moving closer to us, and the Andromeda Galaxy is expected to "collide" with the Milky Way at some future point.
Further away galaxies are receding faster. Light from further away galaxies is older. Does it therefore not follow that the expansion of the universe is slowing down?
Readit News
If measurements point to some sort of incongruity, questioning the accuracy of one's ruler is a fools trap. Altering the rulers to remove incongruities results in a spiral of compromises, internal debates that don't result in progress. If one suspects that the rulers are wrong, the answer is to build a better ruler. Not to arbitrarily chop bits off until the difficult observations go away.
I have no doubt that there are great scientist spending their entire careers trying to improve these rulers and measurements, but I also know that there are great scientists spending their entire careers basing everything on the best rulers they have...
> That brings her value into statistical agreement with recent measurements from the cosmic microwave background, which is 67.4, plus or minus 0.7%.
Does it? As a lay person who can do basic arithmetic, this seems incorrect? Maybe there is some rounding or truncation, since I didn't check the source paper, or maybe I don't understand how confidence intervals work.
`70.4 × 0.97 = 68.288` and `67.4 × 1.007 = 67.8718`
These numbers are certainly close, but to my naive interpretation, the ranges don't overlap?
As is typical, the tolerances given are sigma values for an assumed normal distribution, not the width of a uniform distribution. The disagreement is less than five sigma, so (in the domain of physics) the disagreement is not considered significant enough to be a high-confidence indicator of new physics.
For a null hypothesis of “their differences are consistent with zero”, the p-value is 17%, equivalent to a 1.4 sigma difference. That’s pretty far from a reasonable rejection criterion for the null hypothesis. I think most people would agree that that means these measurements are plausibly consistent.
https://archive.ph/HuLlG
It's amazing just rich the electromagnetic spectrum is for analyzing the universe, from radio to X-rays, and how complementary the pictures are. Though we get visually pleasing pictures in the visible spectrum, most of the really intellectually pleasing stuff of the past century has been outside the visible range.
I'm not a physicist, but from my understanding, the situation is a bit more complicated than the phrasing in your question suggests.
Observation #1: The light from far-away galaxies is redshifted (spectral lines are a bit off from where we'd expect them to be). This suggests that these galaxies are moving away from us. The farther away the galaxy, the more it is redshifted. This suggests that the farther away the galaxy, the faster it is moving. Observations indicate that the recession speed is directly proportional to distance.
This observation is consistent with general relativity, which suggests an expanding universe with homogeneous mass.
But on a smaller scale, gravitational binding somehow takes over, and on even smaller scale, things like electromagnetic and nuclear interactions start having a greater impact, and that's why the Milky Way isn't itself expanding. For that matter, even Andromeda (0.8 Mpc) is too close to be affected by Hubble-style expansion, which only becomes observable at the multi-megaparsec scale.
It's a bit of a misnomer though, because it's only constant through space, not time. At the time of discovery it was assumed to be constant in time, too.
Imagine inflating a balloon onto which you've painted dots. All the dots move apart. But the ones furthest apart move apart faster than those close together. This is how you know the dots aren't just moving in their local environment, the entire space is expanding (everywhere).
(If you want a 1D representation, move your fingers apart at a constant rate. Consider how much further apart your pinky and index finger are compared with your middle and ring finger. That wouldn't happen if you just make a Spock hand.)