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+ - How does matter cool in an expanding Universe?

Submitted by StartsWithABang
StartsWithABang (3485481) writes "If the Universe is expanding and cooling, it’s easy to visualize how radiation cools: it has a wavelength, space expands, and so as the wavelength gets stretched, the energy drops. But what about the matter? Energies must have dropped for matter as well, otherwise it wouldn’t have lost enough kinetic energy to become gravitationally bound into gas clumps, stars and galaxies. And yet, those things very much exist! What’s the resolution to this? The incredible answer is here."

+ - Giving thanks, the astrophysicist's way

Submitted by StartsWithABang
StartsWithABang (3485481) writes "Today (Thursday), the fourth Thursday of November, marks American Thanksgiving, an annual harvest festival and feast where we celebrate a variety of things, particularly the good things that have come to us in life. And yet, what’s amazing is that—if you’re willing to start with expanding spacetime and the laws of physics—a Universe that looks a whole lot like ours, complete with clusters, galaxies, stars, planets, heavy elements, and, most probably, life, is inevitable. And it’s inevitable all over the Universe. Be thankful for that!"

+ - The future of low-Temperature physics

Submitted by StartsWithABang
StartsWithABang (3485481) writes "With every extra digit we add in our quest for absolute zero, more and more of the Universe becomes accessible to us. One of the holy grails of this will be to measure the inherent line width of the spin-flip transition of atomic hydrogen, perhaps the narrowest of all emission lines. If we can go even deeper than that, probing its structure over time, we could wind up seeing signatures of phenomena such as gravitational waves, a time-varying gravitational constant or black hole formation. We're waiting on the experimentalists to get us there, but in theory, this is happening all the time."

+ - The highest and lowest energy signals from the Universe

Submitted by StartsWithABang
StartsWithABang (3485481) writes "Accelerated by some unknown mechanism, the highest energy particles in the entire Universe come from all over the sky with energies exceeding 10^19 eV, or more than a million times the energies achieved at the LHC. On the flipside, the lowest energy radio waves are emitted by an ultra-rare transition of hydrogen atoms, and may provide a window into the Universe from before the first stars formed. Come learn about the highest and lowest energy signals from the Universe, and why they matter for our understanding of it all."

+ - The origin of life requires dark matter

Submitted by StartsWithABang
StartsWithABang (3485481) writes "When you think of the origin of life, you probably think about the atoms coming together to make molecules, the molecules coming together to make self-replicating, information-encoded strands, and how all that took place here on Earth. But you might want to consider a different point of view. Try thinking about the fact that those complex atoms need to be created and recycled into new generations of stars, which requires stars to live, die, expel that processed matter back into the interstellar medium, and to have it incorporated into future generations of star systems. Simply having the primordial ingredients wouldn’t give rise to anything interesting. Without dark matter, the structures enabling this wouldn't have been able to form at all, but with it, everything is possible!"

+ - The Birth of Space and Time

Submitted by StartsWithABang
StartsWithABang (3485481) writes "Finite to the past, infinite to the past, or cyclical in nature: those are the three options for the nature of our spacetime. We can trace our Universe's history back billions of years, to the earliest moments of the Big Bang and even before to the epoch of cosmic inflation that preceded it, but was there truly a singularity from which space-and-time emerged? Here's the limits of our knowledge on that front."

+ - How to see the Universe through our galaxy

Submitted by StartsWithABang
StartsWithABang (3485481) writes "There’s a problem with our view of the night sky: beautiful though it is, we’re incapable of seeing with our own eyes what the Universe is like from an outsider’s perspective. No matter where we are, we’re stuck inside our own galaxy, with all its light-blocking and obscuring properties. But there’s a trick to seeing through it: some wavelengths of light are more transparent to our galaxy’s material than others! And when we get there — when we view it — the rewards are incomparable, including what we learn about what’s there in our own Universe. A great busting of the myth that if we were plunked down at random, we probably wouldn't see a single galaxy."

+ - If Philae were nuclear powered, it'd still be alive today

Submitted by StartsWithABang
StartsWithABang (3485481) writes "After successfully landing on a comet with all 10 instruments intact, but failing to deploy its thrusters and harpoons to anchor onto the surface, Philae bounced, coming to rest in an area with woefully insufficient sunlight to keep it alive. After exhausting its primary battery, it went into hibernation, most likely never to wake again. We’ll always be left to wonder what might have been if it had functioned optimally, and given us years of data rather than just 60 hours worth. The thing is, it wouldn’t have needed to function optimally to give us years of data, if only it were better designed in one particular aspect: powered by Plutonium-238 instead of by solar panels."

+ - Dark energy could be detected directly in a vacuum chamber

Submitted by StartsWithABang
StartsWithABang (3485481) writes "The particles of the standard model, some type of dark matter and dark energy, and the four fundamental forces. That’s all there is, right? But that might not be the case at all. Dark energy may not simply be the energy inherent to space itself, but rather a dynamical property that emerges from the Universe: a sort of fifth force. This is speculation that's been around for over a decade, but there hasn't been a way to test it until now. If this is the case, it may be accessible and testable by simply using presently existing vacuum chamber technology!"

+ - Why spiral galaxies will never be the largest

Submitted by StartsWithABang
StartsWithABang (3485481) writes "The largest galaxies in the Universe all have a few things in common: they all contain many trillions of stars, they all contain many times their stellar mass in the form of dark matter, and they’re all found towards the centers of great galactic clusters. Oh, and one more thing: none of them are spiral galaxies! Why are the largest spiral galaxies in the Universe only a few times the size of our Milky Way, but the largest galaxies overall are hundreds or even a thousand times as big as our home galaxy? The astrophysics behind the largest galaxies in the Universe."

+ - For quantum theory, the Multiverse is irrelevant

Submitted by StartsWithABang
StartsWithABang (3485481) writes "For centuries, the argument has raged about whether light is — at its fundamental core — a wave or a particle. More recently, not only have all the fundamental particles gotten in on that argument, but also about which interpretation of quantum mechanics is the right one. Are there many parallel Universes? Is the Universe in an indeterminate state? Are there nonlocal, hidden variables determining everything? Or — with the original formulation — did Niels Bohr have it right all along? As it turns out, these may not even be the right questions to be asking; if they all give the same observational predictions, we may be learning only about our own preconceptions by favoring one interpretation over another."

+ - Why landing on a comet is amazing

Submitted by StartsWithABang
StartsWithABang (3485481) writes "Launched from the Rosetta satellite, on a mission 10 years in the making, the space probe Philae just successfully landed on a comet, the first time in history humanity has managed to make such a thing happen. But other than sounding cool, what have we gained? Here's a redux of the technical challenges and achievements, the scientific knowledge to come and when we can expect the payoff!"

+ - Why we don't have time travel, warp drive or hoverboards

Submitted by StartsWithABang
StartsWithABang (3485481) writes "When our science fiction fills our heads with ideas that could make our lives tremendously improved, we like to believe it’s only a matter of time before technology catches up with our imaginations. Indeed, tricorders, wireless communicators and rocket ships were just some of the breakthroughs predicted by sci-fi on their way to becoming commonplace technology. But many of our dreams are a long way from becoming reality, including human-sized teleporters, wormholes and time travel. Here's what happens when science fiction runs into the cold, hard wall that is scientific reality."

+ - The largest Kuiper Belt object isn't Pluto OR Eris

Submitted by StartsWithABang
StartsWithABang (3485481) writes "Out beyond Neptune, the last of our Solar System’s gas giants, the icy graveyard of failed planetesimals lurks: the Kuiper Belt. Among these mixes of ice, snow, dust and rock are a number of worlds — possibly a few hundred — massive enough to pull themselves into hydrostatic equilibrium. The most famous among them are Pluto, the first one ever discovered, and Eris, of comparable size but undoubtedly more massive. But there’s an even larger, more massive object from the Kuiper Belt than either of these, yet you never hear about it: it’s Triton, the largest moon of Neptune, a true Kuiper Belt object!"

+ - The gravitational force doesn't have an infinite range after all 1

Submitted by StartsWithABang
StartsWithABang (3485481) writes "One of the things we learn about the gravitational force is that it has an “infinite range” to it. Because it’s a ~1/r^2 force, and because as you move radially away from the source, a sphere spreads out (in surface area) as ~r^2, you don’t lose anything as you move farther and farther away. So long as you intercept the same angular size on the sky, you’ll experience the same amount of force. But you can’t move arbitrarily far away from a source and still feel its gravitation! Despite being an infinite range force, our Universe has only been around a finite amount of time, and signals only propagate at a finite speed. Here's the reconciliation of these two seemingly contradictory facts."

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