Dark energy highlights continued

Here is a great dark energy FAQ from Sean Carroll, a physicist at CalTech.

Einstein's greatest blunder (?)

In 1917 Einstein added a fudge factor, the cosmological constant, to the equations in his theory of general relativity. Before adding the constant, his equations showed the attractive force of gravity would cause the universe to implode in a Big Crunch. The constant kept Einstein's picture of the universe static – neither expanding nor contracting.

When Edwin Hubble discovered that the universe was expanding (the rate of expansion is what won this year's Nobel Prize), Einstein threw out the cosmological constant, declaring it his greatest blunder.

But the cosmological constant may still work. In fact, without the constant, the age of the universe is calculated to be much younger than the oldest observed stars. Since this makes no sense, the constant may hold validity.

How do spacetime and quantum field theory ultimately fit together? That has been the big looming question. One proposed “quantum correction” to classical mechanics is quantum mechanical vacuum energy. If there is such a vacuum energy, it may be associated with the cosmological constant.

But there is still an incredibly gaping margin of error: when physicists calculated the vacuum energy they came up with an answer 120 orders of magnitude (10^120 times) greater than what we actually observe. It would take me 2 minutes just to write out all those zeroes.

(hey you physics people, want to delve further?)

With all the advances in modern physics and the accomplishments highlighted by this year's Nobel Prize, there still remains an entire universe (or perhaps multiverses?) of mysteries.

Into the Future...

For the time being, budget cuts caused NASA to scrap its projects investigating dark energy using the James Webb Telescope. Fortunately, in 2019 the European Space Agency plans to step in with its Euclid mission.

The Large Synoptic Survey Telescope (LSST) in Chile will become another source of data for dark energy research.

Dark energy gets attention from Nobel Prize in Physics

*picture from NASA

Three American-born physicists won the Nobel Prize in Physics on Tuesday. Thirteen years ago they first made the startling announcement that the universe is expanding at an accelerating rate. They made the discovery by measuring the brightness of type 1a supernovae, explosions of small stars known as white dwarfs that can outshine an entire galaxy and can radiate as much energy as our sun will in its entire lifetime. The measurements showed that the supernovae were dimmer than what was expected, suggesting that galaxies were moving apart at an increasing rate.

At the time scientists were skeptical of the results – the prevailing view was that the universe was slowing down in its expansion. Yet two teams in competition with each other (one led by Saul Perlmutter of the Lawrence Berkeley National Laboratory, and the other headed by Brian Schmidt of the Australian National University in Canberra and Adam Reiss of the Space Telescope Science Institute and Johns Hopkins University) used independent lines of evidence to reach the same results.

The Nobel Prize brings attention to the study of a mysterious component of the universe called dark energy.


What is dark energy?

The simple answer: we don't really know, but physicists believe that dark energy is the “thing” that causes the universe to accelerate in its expansion. It's a little unbelievable that dark energy makes up about 73% of the universe, and yet we know so little about it. There are three properties to note. First, look at the name: dark. It is 'dark' because we don't see it; we do not observe dark energy interacting with matter at all. Second, it is smoothly distributed. The density of dark energy is uniform throughout space. And third, it is persistent. Unlike particles of matter, dark energy doesn't cluster together or dilute away.

The difference between dark energy and dark matter

Dark energy is not the same thing as dark matter. Again, look at the name. Dark energy is energy – it doesn't consist of particles. Dark matter consists of particles of matter. Physicists think it's there but they have yet to directly detect the particles.  However, they have observed gravitational influences (in settings like galaxies, clusters, large-scale structure, and microwave background radiation) that they attribute to clusters of dark matter.

Dark matter makes up about 23% of the universe. Actual matter – the stuff that the Earth is made up of, and the stuff that you and me interact with on a day-to-day basis – makes up less than 5% of the universe. Crazy.

More to come soon...