How Does Our Earliest Picture Of The Universe Show Us Dark Matter?
“So all you need to do, to know whether your Universe has dark matter or not, is to measure these temperature fluctuations that appear in the CMB! The relative heights, locations, and numbers of the peaks that you see are caused by the relative abundances of dark matter, normal matter, and dark energy, as well as the expansion rate of the Universe. Quite importantly, if there is no dark matter, you only see half as many total peaks! When we compare the theoretical models with the observations, there’s an extremely compelling match to a Universe with dark matter, effectively ruling out a Universe without it.”
If your young Universe is full of matter and radiation, what happens? Gravitation works to pull matter into the overdense regions, but that means that the radiation pressure must rise in those regions, too, and that pushes back against the matter. On small scales, this pushback washes out the gravitational growth, but on large-enough scales, the finite speed that light can travel means that no wash-out can happen. Dark matter, however, doesn’t collide with radiation or normal matter, while normal matter collides with both radiation and itself. If we can calculate exactly how these three species interplay, we can calculate what types of patterns we expect to see in the Big Bang’s leftover glow, and then compare it with what we observe with satellites like WMAP and Planck. And what have we seen, exactly, when we’ve done that?
Ask Ethan: How Close Could Two Alien Civilizations Get To One Another?
“What’s [the] closest two, independent intelligent civilizations could be, ignoring interstellar travel and assuming they develop in different star systems and follow roughly what we know as ‘life’? Globular clusters can have a high density of stars, but does too high a density rule out habitability? An astrophysicist in a dense cluster would have a much different view of the universe and the search for exoplanets.”
Okay, so you have a planet that has the right ingredients for life, and everything has worked out according to your wildest dreams. We’ve developed life, it’s thrived for billions of years, and now we’ve reached the point where we’ve got an intelligent, technologically advanced civilization, just like we do here on Earth. Let’s imagine we’ve got multiples, now, throughout the Universe. What’s the closest two independent ones could possibly be? Should we look in the same solar system? In a globular cluster? In the galactic center? In a spiral arm? In an open star cluster? Or should we just wait for another one to pass close by in interstellar space?
Could Artificial Intelligence Solve The Problems Einstein Couldn’t?
“There are some things that machines are better at than humans. The number of calculations a machine can perform, along with the speed it can perform them, vastly outstrips what even the most brilliant geniuses among us can do. Computer programs have, for many decades now, been able to solve computationally intensive problems that humans cannot. This isn’t just for brute force problems like calculating ever-more digits of π, but for sophisticated ones that were once unimaginable for a machine.
No top human has defeated a top computer program at chess in over a decade. The technology that Apple’s Siri is based on grew out of a DARPA-funded computer project that could have predicted 9/11. Fully-autonomous vehicles are on track to replace human-driven cars within the next generation. In every case, problems that were once thought best-tackled by a human mind are giving way to an AI that can do the job better.”
We normally conceive of genius as a uniquely human trait. We can forge connections between disparate fields, make analogies and see patterns that are enabled by our experience, and apply what we know in one arena of life to entirely different, unrelated problems. It was this realization that led Einstein to state his now-famous remark that “imagination is more important than knowledge.” Yet here in the 21st century, all these things are no longer unique to humans: artificial intelligence is doing these exact things. In many cases already, from exoplanet hunting to predicting new states of quantum matter, it’s doing them at a level that far outstrips what humans can do alone. Are there any problems at all that humans are absolutely required for, or will AI someday do it all?
Ask Ethan: Could The Universe’s Missing Antimatter Be Found Inside Black Holes?
“It is a mystery why we see matter without corresponding antimatter. Some remote and old super massive black holes evolved much faster than current theory is able to predict. Could the missing antimatter be hiding inside those primordial black holes? Does the total mass of super massive black holes come even close to the amount of missing anti matter?”
When we look out at the Universe today, we see that everything is made of matter and not antimatter. This is a puzzle, because the laws of physics appear to be symmetric between matter and antimatter: you can’t create or destroy either one without creating or destroying an equal amount of the other. Is it possible that we actually created equal amounts of both, and that the antimatter collapsed into black holes, which might be responsible for either supermassive black holes or primordial black holes as dark matter? While, on the other hand, the normal matter didn’t collapse, and became the stars, gas, galaxies, and more that we observe today?
“The first Friedmann equation describes how, based on what is in the universe, its expansion rate will change over time. If you want to know where the Universe came from and where it’s headed, all you need to measure is how it is expanding today and what is in it. This equation allows you to predict the rest!”
In 1915, Einstein put forth General Relativity as a new theory of gravity. It reproduced all of Newton’s earlier successes, solved the problem that Newton couldn’t of Mercury’s orbit, and made a new prediction of bent starlight by large masses, verified during the 1919 solar eclipse. Despite the fact that it included a cosmological constant to keep the Universe static, that didn’t deter Soviet physicist Alexander Friedmann from solving Einstein’s equations for a Universe that was filled with matter and energy, all the way back in 1922. The two generic equations he found, known as the Friedmann equations, immediately related measurable quantities like the amount of matter in the Universe to the expansion or contraction rate, which just years later became validated by Hubble’s observations. But the young Friedmann never lived to see it; he died of typhoid fever contracted when he was returning from his honeymoon in 1925.
What Astronomers Wish Everyone Knew About Dark Matter And Dark Energy
“It wasn’t always apparent that this would be the solution, but this one solution works for literally all the observations. When someone puts forth the hypothesis that “dark matter and/or dark energy doesn’t exist,” the onus is on them to answer the implicit question, “okay, then what replaces General Relativity as your theory of gravity to explain the entire Universe?” As gravitational wave astronomy has further confirmed Einstein’s greatest theory even more spectacularly, even many of the fringe alternatives to General Relativity have fallen away. The way it stands now, there are no theories that exist that successfully do away with dark matter and dark energy and still explain everything that we see. Until there are, there are no real alternatives to the modern picture that deserve to be taken seriously.”
If you yourself are not a professional astronomer or astrophysicist, you might feel in your gut that dark matter and dark energy just can’t be right. How could we possibly conclude that only 5% of our Universe is made out of the matter that everything we know of is composed of, and that 95% of the Universe is made of some dark substance we’ve never successfully detected. It sounds crazy, and therefore, you wonder, isn’t there some simpler explanation that’s likely correct? It’s not just you: the professionals have wondered this, too. And if there is, it means we have to throw out all of the successes we’ve achieved so far. So goodbye, General Relativity. Goodbye to the Big Bang, to astrophysics, to structure formation, to what we know about stars and galaxies, to gravitational lensing, to gravitational waves, and so much more. To get rid of dark matter and dark energy, we have to throw out the baby with the bathwater.
‘Losing The Nobel Prize’ Makes A Good Point, But Misses A Great One (Book Review)
“This is science. Our goal is to fully understand the Universe, one incremental step at a time. Our human failings are many, and we must not let them get the best of us. In Losing the Nobel Prize, Brian Keating exposes not only the failings of the Nobel Prize system, but also his own personal frailties. What emerges is a flawed but sympathetic read, where you’ll find yourself rooting not only for quality science to win out in the end, but for every contributor to work together in an open fashion for the benefit of human knowledge in general. We may be a long way from achieving that goal, but it’s arguable that by losing the Nobel Prize, Keating and BICEP2 has led us to an even greater victory: the recognition that there are more important things in this Universe, like scientific truths, than the fleeting glory of an earthly award.”
Imagine that you stake your life’s work on a high-risk, high-reward proposition. You think you’ve got a great new way to push the limits on our understanding of the Universe to never-before-probed frontiers. If you succeed, which is to say, if you’re first to probe that, and you find something new and novel, you’ve just made a tremendous scientific breakthrough. If you play the publicity game right, your research, its implications, and quite possibly, you, might be deemed Nobel-worthy. Only three people, maximum, can ever wind the Nobel Prize for a particular discovery, despite the fact that dozens, hundreds, or even thousands of people are required to bring such an experiment to fruition. Now imagine you did that, got the spectacular result, and then had your finding overturned, as the field found your work to be sloppy, premature, and incomplete.