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New, Higher Measurement of Universe's Expansion May Lead To a 'New Physics' (space.com)
doug141 writes: Astronomers have measured the universe's current expansion rate (a value known as the Hubble constant) at about 44.7 miles (71.9 kilometers) per second per megaparsec (3.26 million light-years). This is consistent with a calculation that was announced last year by a research team, but it's considerably higher than the rate that was estimated by the European Space Agency's Planck satellite mission in 2015 -- about 41.6 miles (66.9 km) per second per megaparsec. The cause of this discrepancy is unclear. "The expansion rate of the universe is now starting to be measured in different ways with such high precision that actual discrepancies may possibly point towards new physics beyond our current knowledge of the universe," a researcher said. Mike Wall writes via Space.com: "The differences in the Hubble constant estimates may reflect something that astronomers don't understand about the early universe, or something that has changed since that long-ago epoch, scientists have said. For example, it's possible that dark energy -- the mysterious force that's thought to be driving the universe's accelerating expansion -- has grown in strength over the eons, members of Riess' team said last year. The discrepancy could also indicate that dark matter -- the strange, invisible stuff that astronomers think vastly outweighs 'normal' matter throughout the universe -- has as-yet-unappreciated characteristics, or that Einstein's theory of gravity has some holes, they added."
The Hubble parameter hasn't been considered constant for a very, very long time. It would only be constant in a deSitter space - where the only energy density is the cosmological constant. The value of the Hubble is determined by Friedmann's equation in terms of the (evolving) energy densities associated with matter, radiation, dark energy, dark matter etc.
H= 8\pi/3 (rho)
where rho is the energy density - this changes as the universe expands as the energy densities of matter components change under expansion (matter is diluted, radiation is diluted and red-shifted, cosmological constant stays constant etc).
This is one of the "many more measurements". Basically, there are two traditionally two ways to measure the Hubble constant: from supernovae, and from the CMB. Recently (i.e. the past few years) these two sets of measurements have disagreed about the value, with the CMB measurement shooting lower, and supernovae shooting higher, and both sides of the debate having good reasons to doubt the other. This looks to be a method independent of both of the others, which is a really good thing. Not that the linked article explains this, or gives a link to the damned paper which would probably explain this itself.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
Indeed. When I'm debugging a program and feed it new data and something completely unexpected (and obviously off-the-wall) comes out the other side, I always ask myself "Wait, what am I assuming?".
This is what drives me absolutely batshit about modern cosmology:
I believe you. What this points out however is that you are completely unsuited for modern cosmology. That isn't trying to be insulting, as not many people are not.
The problem with cosmology is that we are not "there". We are not present at the birth of the universe, we are not in an early galaxy, we do not have people across the universs who can communicate with us to inform us of just what is what.
So there has to be assumptions. Otherwise we are left with the idea that the sky is a upside down bowl with holes in it, or that the stars are the souls of our ancestors looking down on us (I'll return to that in a minute)
So now these assumptions. Wild-ass guesses, some of them. In fact, that upside down bowl and ancestors concept was indeed cosmology, and two wild-ass guesses. Assumptions long since proven untrue. And cosmology is littered with this:
Ptolemaic system, Geocentric universe, Heliocentric Universe, Copernican system, Newtonian Gravity, Steady State Universe. In the middle of this there was the concept of luminiferous aether, which comes closest to a modern wild ass guess.
As each model was superseded by knowledge learned, it was abandoned. It doesn't mean that the people of science who did all the previous work were idiots. It was just that we learned more. In earlier times, there were so many more assumptions. And facts were slow coming in. But when a fact destroyed an assumption, the assumption had to go.
side note: I want to approach this delicately, but there are many real world cases of people and groups of people who demand to hold on to earlier assumptions in the face of facts.
And in the world of cosmology, the previous and wrong cosmology is not bad, or even useless. It becomes a placeholder, a basis to do further research. If we just threw up our hands and gave up at every thing we do not know, there would be no research. So we'd be praying to those little dots of light in the sky - maybe, because that is a cosmological assumption as well. Or may just looking at them with no thoughts of any kind. Is that what you would prefer?
The shepherds did so well protecting the flock that the sheep no longer believed that wolves existed.
Many apologies, that should be H^2 = 8\pi \rho/3...
I don't know all the ramifications (as I don't work in either CMB or distance measurement astrophysics), but the difference is pretty small (the Planck measurement was ~67 1/(km*Mpc), compared to this which was 72 1/(km*Mpc)). This measurement, now I look at the actual numbers, is actually closer to the measurement most of the CMB experiments have gotten (Planck got lower than most, albeit with smaller error bars). FWIW, the measurements are all a few standard deviations away from each other (as a rule you need more than 5 standard deviation for results to really be considered in disagreement), so really it's not a major discrepancy.
If the CMB measurement turns out to be wrong, it *could* indicate some interesting new physics (modified gravity, some new species of dark matter, dark energy doesn't behave quite like we think it does, that kind of thing) which would be very interesting indeed. But, we're still a ways away from being able to say that with any certainty.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton