Dark matter and dark energy are staples of current pop science, even though we have never found either. So we asked our physics color commentator Rob Sheldon, what’s the evidence base for either of them, really?
Hey, it would be fun to believe but then it would be fun to believe in Santa Claus. What does the evidence suggest? So he wrote back to say:
Dark Matter (DM) and Dark Energy (DE) have very different epistemic support. In fact, DE was originally called “the cosmological constant” or “Lambda” and was renamed DE in order to achieve higher status by sounding like a twin to DM.
Fritz Zwicky back in 1935 was the first to point out that galaxies are spinning fast enough to “throw out” the stars on the outer edges. That is, calculating the gravity of the glowing stars in the center of the galaxy did not account balance the “centrifugal” force on the outer stars. Some extra gravity must be holding them in, and most attributed it to black holes and/or dust—hence “dark”. In 1975 Vera Rubin did a careful survey of the nearest disk galaxy to us—the Andromeda Galaxy—and measured the speeds of individual stars, showing that indeed Zwicky’s low resolution data was correct. Surveys throughout the 90’s looking for dark matter–hydrogen gas clouds, dust clouds, stellar mass black holes—all came up empty. They found some dark stuff, but not enough of it. That’s when the supercollider in Texas was cancelled, and a few 1000 particle physicists were out of work, who somehow decided that finding “particulate” dark matter was just as exciting. Hence the 100 or so particle experiments such as LUX, etc., looking for exotic particles.
Although none of these particle experiments have succeeded, the astronomy data is stubbornly real. Unfortunately in much of the popular press, the astronomy data fades into the background, and all we hear about is the latest exotic particle theory. My own view on this, is that DM is not an exotic particle (hence the failed experiments), but rather small astronomical bodies smaller than asteroids and bigger than a pea, otherwise known as comets. They match all the known properties of DM, failing only to fit into models of the “standard” Big Bang cosmology. My goal has been to show that it is possible to add them to the models by creating copious comets from the very beginning, say, the first millennia of the BB, and not have to wait for 100 million years for trace amounts.
The epistemic support for this concept is very weak. Einstein added an “anti-gravity” term to his famous General Relativity equations, because otherwise gravity would collapse the universe into a monster black hole. Many people pointed out to him that by making his anti-gravity term proportional to volume, it was unstable—if the universe got a bit bigger it would overwhelm the matter, or if the universe got a bit smaller, matter would win and we’d end up a black hole again.
When Edwin Hubble showed that the universe was expanding, Einstein realized that kinetic energy solved his stability conundrum, and he didn’t need anti-gravity. He deleted it from his equations, calling it his biggest blunder.
Thirty years after his death, the Big Bang modellers were unable to get their codes to look like the astronomy data—lacy filaments of galaxies stretched out through 3D space. Their codes were making blobs or puffs without the filaments. By reintroducing Einstein’s anti-gravity, now renamed Dark Energy, they got the codes to work, and began to petition astronomers to find evidence of it. Like a lot of things, word on the street was that the discoverer would get the Nobel Prize.
Saul Perlmutter, Adam Riess & Brian Schmidt were young and hungry astronomers who picked up the gauntlet. With 74 supernovae data sets and a lot of massaging, they claimed to have found evidence of an accelerating universe, aka anti-gravity. By 2011 they had the Prize, and now the data analysis is falling apart. Read or watch Sabine Hossenfelder’s interview with Oxford cosmologist, Subhir Sarkar earlier this year. It is very revealing. [below]
My takeaway is that DE is “pathological science,” using the words of Irving Langmuir to describe N-rays or polywater. It is science at the edge of messy data, finding what one is looking for by using poor statistical methods. It is precisely what astronomers are trained NOT to do, and therefore this whole Nobel Prize thing is a corruption of what had been a relatively unstained field.
If you want more insight into the astronomical community concerning both Dark Matter and Dark Energy, I recommend Stacy McGaugh’s blog, Triton Station, particularly his post on Dark Energy, “A personal recollection of how we learned to stop worrying and love the Lambda”
If you haven’t heard me say it before, the crisis in physics (or cosmology, or biology) is not that “God is subtle” or “Nature is perverse”, but rather because scientists love the praise of men rather than the truth.
Rob Sheldon is the author of Genesis: The Long Ascent and The Long Ascent, Volume II
2 Replies to “Rob Sheldon dishes on dark matter and dark energy”
Why is this “dark matter / dark energy” thing so intriguing?
As I understand it, if our understanding of gravity is correct, the Universe is observed to behave in ways that cannot be explained by the matter we can see. There has to be something else there influencing that behavior that we do not see, hence, dark matter and dark energy. Either that or the Force is strong in this Universe.