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General Relativity
For decades, theorists have been cooking up "theories of everything" to explain our Universe. Are all of them completely off-track?
On cosmic scales, only dark matter (or something equivalent) gives us the Universe we observe. Now, the Sunyaev-Zel'dovich effect agrees.
We have two descriptions of the Universe that work perfectly well: general relativity and quantum physics. Too bad they don't work together.
When what we predict and what we measure don't add up, that's a sign there's something new to learn. Could it be a new fundamental force?
The combination of charge conjugation, parity, and time-reversal symmetry is known as CPT. And it must never be broken. Ever.
In theory, the fabric of space could have been curved in any way imaginable. So why is the Universe flat when we measure it?
Binary black holes eventually inspiral and merge. That's why the OJ 287 system is destined for the most energetic event in history.
Nothing lives forever, at least, not in the known Universe. But relativity allows us to get closer than ever: from a physics perspective.
Not everyone accepts the scientific consensus; some even make careers out of challenging it. But only a select few do it the right way.
Quantum entanglement links information between particles across space and time. So what happens when one of them falls into a black hole?
The Universe is expanding, the expansion is accelerating, and some galaxies even recede faster-than-light. Can we see a change in real time?
Even the most brilliant mind in history couldn't have achieved all he did without significant help from the minds of others.
Even at its faintest, Venus always outshines every other star and planet that's visible from Earth, and then some!
Our great hope is that today's indirect, astrophysical evidence will someday lead to successful direct detection. What if that's impossible?
Even in an expanding Universe, we expect both redshifted and blueshifted galaxies. But nearly every one we see is redshifted. Here's why.
Two main contributors enabled our modern global positioning system (GPS): Albert Einstein and Gladys West. Here's how she made it happen.
Many view the development of fringe, alternative theories as a useless waste of time. But when they can be tested, it shows what reality is.
Gravitational lenses arise when foreground masses and background light sources properly align. Einstein rings are rare, but crosses abound.
It's not about particle-antiparticle pairs falling into or escaping from a black hole. A deeper explanation alters our view of reality.
The VENUS survey isn't about planets at all, but about finding multiply-lensed supernovae. The ambition? To save the expanding Universe.
In general relativity, matter and energy curve spacetime, which we experience as gravity. Why can't there be an "antigravity" force?
Particles are everywhere, including particles from space that stream through the human body. Here's how they prove Einstein's relativity.
From white holes to dark stars and multiverses, James Riordon explores the bizarre exhibits of general relativity's "cryptozoo."
We first measured G, the gravitational constant, back in the 18th century. As the least well-known fundamental constant, can it be improved?
In 2017, a kilonova sent light and gravitational waves across the Universe. Here on Earth, there was a 1.7 second signal arrival delay. Why?
The planet, the Solar System, and the galaxy aren't expanding. But the whole Universe is. So where does the dividing line begin?
We've long known we can't go back to infinite temperatures and densities. But the hottest part of the hot Big Bang remains a cosmic mystery.
Observations with the Hubble space telescope helped cement dark energy and reveal the Hubble tension. How are these two things so different?
Inflation's two main criticisms, that it can predict anything and that the "measure problem" remains unsolved, can't erase its successes.
As the Universe ages, it continues to gravitate, form stars, and expand. And yet, all this will someday end. Do we finally understand how?