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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."
What, they were standing on a skyscraper when they measured it?
Sig?
In other news "new independent measure of hubble constant shows possible difference from previous measurement. Many more measurements and peer review and theory to follow slowly. But this won't give clicks and excitement so we'll exaggerate things as much as possible please click please click please click please..."
1) The speed of light is constant, everywhere and everywhen.
Variable Speed of Light theories, around for 20-30 years. Investigated in cds.cern.ch/record/618057/files/0305457.pdf
Current observations put very very very tight bounds on dc/dt.
2) The gravitational constant is the same, everywhere and everywhen.
Jordan-Brans-Dicke theories. Hundreds of papers, dating back to Dirac's large number hypothesis. See http://www.scholarpedia.org/ar...
3) The shape of space is uniformly flat, everywhere and everywhen.
No. Space-time is a curved manifold. Not only in the cosmological (isotropic+homogeneous limit) with limiting spaces of three-spheres or hyperbolic spaces, but also across huge perturbations on them. See https://arxiv.org/abs/1501.038... for tests of homogeneity and isotropy, for example.
4) Please don't get me started about standard candles.
OK, I won't. They conform with observations, match the fine-stucture constant and Lyman forest predictions incredibly well, vast literature that exists on these matches cosmic helium and hydrogen observations, matches with galactic rotations etc.
5) Or cosmological inflation.
Producing effects as predicted. See https://arxiv.org/abs/1311.165... for an in depth probability test of cosmological parameters including the spectral tilt and scalar to tensor ratio of perturbations (CMB) predicted by inflation.
6) Or the (luminiferous) aether. Sorry, the Higgs field/particle/whatever.
Predicted, observed, behaving exactly as predicted at 5 sigma significance in the mass.
Just because YOU don't know about it, doesn't mean that we haven't investigated it. But of course, feel free to keep having a reckon without looking stuff up first.
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).
The thing that blows my mind is not that one measurement is higher and another lower, it's just how closely they agree: to less than 10%. This despite the fact that they were arrived at from different instruments and lines of inquiry. The earlier measurement from Planck satellite measurements is derived from measurements of cosmic background radiation. The newer measurement comes from images of gravitational lensing of distant quasars, from the Hubble and Spitzer telescopes. For such a tricky measurements, and such an abstruse topic, I wouldn't have been surprised if they differed by an order of magnitude.* And yet, the agree pretty closely.
Science is really freaking awesome. Sure, assuming that the expansion is universal and constant (i.e., there is only one value for the Hubble Constant, which is hardly a sure thing), you ought to be able to measure the same answer by any experiment designed to measure it, within the experimental error. I ought to arrive at the same value for the gravitational constant, too, whether I experiment using a precision pendulum, or dropping a cannonball from the tower of Pisa (accounting for air friction, of course), or analyze the tides, or by successfully putting a man on the Moon. It doesn't matter who I am, or where I live, or under which government, or what language(s) I speak - it all still works.
* Hubble's own initial estimate was about 10x the current values. For those that are interested, here's a graph of the value of H0, with error bars, through history. [source]
There once was a stargazer named Hubble,
Who said, "We expand like a bubble!"
But finding the rate,
Was a source of debate,
Contention, dissension, and trouble.
In a land where tornadoes are wormholes to alternate dimensions, you've got to have all kinds of weird physics going on.
The Quirkz Handbook of Self-Improvement for People Who Are Already Pretty Okay
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.