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Big Bang Theory
Astronomy's roots rest in the very origins of humanity. We have always looked to the skies for answers. We are starting to get them.
At all distances, the Universe expands along our line-of-sight. But we can't measure side-to-side motions; could it be rotating as well?
No matter how beautiful, elegant, or compelling your idea is, if it disagrees with observation and experiment, it's wrong.
The Universe is expanding, and the Hubble constant tells us how fast. But how can it be a constant if the expansion is accelerating?
13.8 billion years ago, the hot Big Bang gave rise to the Universe we know. Here's why the reverse, a Big Crunch, isn't how it will end.
In Sun-like stars, hydrogen gets fused into helium. In the Big Bang, hydrogen fusion also makes helium. But they aren't close to the same.
Everything that gets heated up has to, somehow, radiate that energy away. Here's what we see when that happens in the Universe.
Look out at a distant object, and you're not seeing it as it is today. It's size, brightness, and actual distance are all different.
Ancient helium-3 from the dawn of time leaks from the Earth, offering clues to our planet’s formation. A key question is where it leaks from.
For some reason, the charges on the electron and proton are equal and opposite, and their numbers are equal, too. But why?
As far as we can tell, there's no limit to how far it goes on; only a limit to how far we can see. Could the Universe truly be infinite?
For some reason, when we talk about the age of stars, galaxies, and the Universe, we use "years" to measure time. Can we do better?
To answer any physical question, you must ask the Universe itself. But what happens when the answers aren't around anymore?
The James Webb Space Telescope could help scientists learn about the cosmic dark ages and how they ended.
Empty, intergalactic space is just 2.725 K: not even three degrees above absolute zero. But the Boomerang Nebula is even colder.
The laws of physics state that you can't create or destroy matter without also creating or destroying an equal amount of antimatter. So how are we here?
Despite all that we've learned about the Universe, there remain unanswered, and possibly unanswerable, questions. Could "God" be the answer?
The Universe has asymmetries, but that's a good thing. Imperfections are essential for the existence of stars and even life itself.
There are ~400 billion stars in the Milky Way, and ~2 trillion galaxies in the visible Universe. But what if we aren't typical?
The Universe is supposed to be the same everywhere and in all directions. So what's that giant "cold spot" doing out there?
Is the Universe finite or infinite? Does it go on forever or loop back on itself? Here's what would happen if you traveled forever.
It is time to give the Russian cosmologist the credit he deserves.
We frequently say it's 2.725 K: from the light left over all the way from the Big Bang. But that's not all that's in the Universe.
The James Webb Space Telescope finally could answer the age-old question of whether we are alone in the universe.
There are two fundamentally different ways of measuring the Universe's expansion. They disagree. "Early dark energy" might save us.
From before the Big Bang to the present day, the Universe goes through many eras. Dark energy heralds the final one.
Known as primordial black holes, they could thoroughly change our Universe's history. But the evidence is strongly against them.
We know it couldn't have began from a singularity. So how small could it have been at the absolute minimum?
Astrophysicists once believed in a static Universe, containing only the Milky Way galaxy. Science definitively proved otherwise.
After more than two decades of precision measurements, we've now reached the "gold standard" for how the pieces don't fit.