When I put on water for tea, something peculiar happens.
Of course, it happens for everyone, but a lot of people probably don't think about it. For a while, the water quietly heats. It undergoes convection -- the water in contact with the element at the bottom of the pot heats up, and since warmer water is less dense, it rises and displaces the cooler layers above. So there's a bit of turbulence, but that's it.
Then, suddenly, a bit of the water at the bottom hits 100 C and vaporizes, forming bubbles. Those bubbles rapidly rise, dispersing heat throughout the pot. Very quickly afterward, the entire pot of water is at what cooks call "a rolling boil."
This quick shift from liquid to gas is called a phase transition. The most interesting thing about phase transitions is that when they occur, what had been a smooth and gradual change in physical properties (like the density of the water in the teapot) undergoes an enormous, abrupt shift -- consider the difference in density between liquid water and water vapor.
The reason this comes up is that some physicists in Denmark and Sweden have proposed a phase transition mechanism to account for the evolution of the (very) early universe -- and that proposal may solve one of the most vexing questions in astrophysics today.
A little background.
As no doubt all of you know, the universe is expanding. This fact, discovered through the work of astronomer Edwin Hubble and others, was based upon the observation that light from distant galaxies was significantly red-shifted, indicating that they were moving away from us. More to the point, the farther away the galaxies were, the faster they are moving. This suggested that some very long time in the past, all the matter and energy in the universe was compressed into a very small space.
Figuring out how long ago that was -- i.e., the age of the universe -- depends on knowing how fast that expansion is taking place. This number is called the Hubble constant.
This brings up an issue with any kind of scientific measurement, and that's the difference between precision and accuracy. While we use those words pretty much interchangeably in common speech, to a scientist they aren't the same thing at all. Precision in an instrument means that every time you use it to measure something, it gives you the same answer. Accuracy, on the other hand, means that the value you get from one instrument agrees with the value you get from using some other method for measuring the same thing. So if my car's odometer tells me, every time I drive to my nearby village for groceries, that the store is exactly eight hundred kilometers from my house, the odometer is highly precise -- but extremely inaccurate.
The problem with the Hubble constant is that there are two ways of measuring it. One is using the aforementioned red shift; the other is using the cosmic microwave background radiation. Those two methods, each taken independently, are extremely precise; they always give you the same answer.
But... the two answers don't agree. (If you want a more detailed explanation of the problem, I wrote a piece on the disagreement over the value of the Hubble constant a couple of years ago.)
Hundreds of measurements and re-analyses have failed to reconcile the two, and the best minds of theoretical physics have been unable to figure out why.
Perhaps... until now.
Martin Sloth and Florian Niedermann, of the University of Southern Denmark and the Nordic Institute for Theoretical Physics, respectively, just published a paper in Physics Letters B that proposes a new model for the early universe which makes the two different measurements agree perfectly -- a rate of 72 kilometers per second per megaparsec. Their proposal, called New Dark Energy, suggests that very quickly after the Big Bang, the energy of the universe underwent an abrupt phase transition, a bit like the water in my teapot suddenly boiling. At this point, these "bubbles" of rapidly dissipating energy drove apart the embryonic universe.
"If we trust the observations and calculations, we must accept that our current model of the universe cannot explain the data, and then we must improve the model," Sloth said. "Not by discarding it and its success so far, but by elaborating on it and making it more detailed so that it can explain the new and better data. It appears that a phase transition in the dark energy is the missing element in the current Standard Model to explain the differing measurements of the universe's expansion rate. It could have lasted anything from an insanely short time -- perhaps just the time it takes two particles to collide -- to 300,000 years. We don't know, but that is something we are working to find out... If we assume that these methods are reliable -- and we think they are -- then maybe the methods are not the problem. Maybe we need to look at the starting point, the basis, that we apply the methods to. Maybe this basis is wrong."
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