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Universe Expansion
Our thermodynamic arrow of time explains why the entropy of any isolated system always increases. But it can't explain what we perceive.
All telescopes are fundamentally limited in what they can see. JWST reveals more distant galaxies than Hubble, but still can't see them all.
There was a time where no starlight was visible throughout the entire cosmos. That time was short-lived: shorter than astronomers imagined.
Gravitational waves carry enormous amounts of energy, but spread out quickly once they leave the source. Could they ever create black holes?
Traveling back in time is a staple of science fiction movies. But according to Einstein, it's a physical possibility that's truly allowed.
The sharpest optical images, for now, come from the Hubble Space Telescope. A ground-based technique can make images over 100 times sharper.
From the coldest planets to spacecraft that have exited the Solar System, these little-known facts stump even many professional astronomers.
The Universe's history, from cosmic inflation to the Big Bang to the present, is known. But whether it's infinite or not is still a mystery.
Although the Big Bang occurred at an instant in time long ago, we still see the light from it. Will the evidence ever disappear completely?
Known as hypervelocity stars, we originally thought just one would be ejected every 100,000 years. The real number is much greater.
There are two different ways to measure the expansion rate of the Universe, and they don't agree. And no, new measurements don't help.
Is gravity weaker over distances of billions of light-years?
A new all-time record! JWST's discovery of JADES-GS-z14-0 pushes the earliest galaxy ever seen to just 290 million years after the Big Bang.
If you bring too much mass or energy together in one location, you'll inevitably create a black hole. So why didn't the Big Bang become one?
The Universe is precisely dated at 13.8 billion years old, but astronomers claim the Methuselah star is 14.5 billion years old. What gives?
It's 2024, and we still only know of the fundamental particles of the Standard Model: nothing more. But these 8 unanswered questions remain.
The expanding Universe, in many ways, is the ultimate out-of-equilibrium system. After enough time passes, will we eventually get there?
For nearly 25 years, we thought we knew how the Universe would end. Now, new measurements point to a profoundly different conclusion.
In ~7 billion years, our Sun will run out of fuel and die. So will every star, eventually. Here are the different fates they'll encounter.
The mutual distance between well-separated galaxies increases with time as the Universe expands. What else expands, and what doesn't?
The number of planets that could support life may be far greater than previously thought, a recent discovery suggests.
We normally think of dark matter as the "glue" that holds galaxies and larger structures together. But it's so much more than that.
There are many theories of gravity out there, and many interpretations of wide binary star data. What have we really learned from it all?
The evidence that the Universe is expanding is overwhelming. But how? By stretching the existing space, or by creating new space itself?
In 2017, we detected gold being forged in a neutron star-neutron star merger. Now, in 2024, the amounts created simply don't add up.
The most iconic "dark nebula" of all lights up under JWST's infrared gaze. Here's what's newly discovered inside.
Holograms preserve all of an object's 3D information, but on a 2D surface. Could the holographic Universe idea lead us to higher dimensions?
In general relativity, white holes are just as mathematically plausible as black holes. Black holes are real; what about white holes?
From the earliest stages of the hot Big Bang (and even before) to our dark energy-dominated present, how and when did the Universe grow up?
Dark energy is one of the biggest mysteries in all the Universe. Is there any way to avoid "having to live with it?"