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General Relativity
It's possible to remove all forms of matter, radiation, and curvature from space. When you do, dark energy still remains. Is this mandatory?
Taught in every introductory physics class for centuries, the parabola is only an imperfect approximation for the true path of a projectile.
The mass that gravitates and the mass that resists motion are, somehow, the same mass. But even Einstein didn't know why this is so.
The Universe isn't just expansion, but the expansion itself is accelerating. So why can't we feel it in any measurable way?
If you think of the Big Bang as an explosion, we can trace it back to a single point-of-origin. But what if it happened everywhere at once?
The original principle of relativity, proposed by Galileo way back in the early 1600s, remains true in its unchanged form even today.
More than any other equation in physics, E = mc² is recognizable and profound. But what do we actually learn about reality from it?
The Michelson-Morley experiment of 1887, despite expectations, revealed a null result: no effect. The implications were revolutionary.
A recent paper in the journal Physical Review Letters claims to prove that a "kugelblitz" is not possible.
Straddling the bounds of science and religion, Newton wondered who set the planets in motion. Astrophysics reveals the answer.
Just 13.8 billion years after the hot Big Bang, we can see objects up to 46.1 billion light-years away. No, this doesn't violate relativity.
The Bullet Cluster has, for nearly 20 years, been hailed as an empirical "proof" of dark matter. Can their detractors explain it away?
The standard picture of our Universe is that it's dominated by dark matter and dark energy. But this alternative is also worth considering.
On the largest of cosmic scales, the Universe is expanding. But it isn't all-or-nothing everywhere, as "collapse" is also part of the story.
There are many things that separate science from ideology, politics, philosophy, or religion. Follow these 10 commandments to get it right.
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.
From the coldest planets to spacecraft that have exited the Solar System, these little-known facts stump even many professional astronomers.
3mins
Nobel Prize winning physicist Frank Wilczek reflects on Einstein’s greatest contribution.
Is gravity weaker over distances of billions of light-years?
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?
For nearly 25 years, we thought we knew how the Universe would end. Now, new measurements point to a profoundly different conclusion.
The mutual distance between well-separated galaxies increases with time as the Universe expands. What else expands, and what doesn't?
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?
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?
In the 20th century, many options abounded as to our cosmic origins. Today, only the Big Bang survives, thanks to this critical evidence.
The Universe is expanding, and the Hubble constant tells us how fast. But how can it be a constant if the expansion is accelerating?
Yes, the Universe is expanding, but if you've ever wondered, "How fast is it expanding," the answer isn't in terms of a speed at all.