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General Relativity
This measurement is crucial to confirm that one of the assumptions of Einstein’s theory of gravity is valid.
Dark matter hasn't been directly detected, but some form of invisible matter is clearly gravitating. Could the graviton hold the answer?
The matter that creates black holes won't be what comes out when they evaporate. Will the black hole information paradox ever be solved?
When it comes to predicting the energy of empty space, the two leading theories disagree by a factor of 100 googol quintillion.
Newton thought that gravitation would happen instantly, propagating at infinite speeds. Einstein showed otherwise; gravity isn't instant.
When the average person has a "theory," they're just guessing. But for a scientist, a theory is the pinnacle of what we can achieve.
The Universe isn't just expanding, the expansion is also accelerating. If that's true, how will the Milky Way and Andromeda eventually merge?
By probing the Universe on atomic scales and smaller, we can reveal the entirety of the Standard Model, and with it, the quantum Universe.
The first observational evidence showing the Universe is expanding is 100 years old now: in 2023. Here's the story of its 100th anniversary.
Some constants, like the speed of light, exist with no underlying explanation. How many "fundamental constants" does our Universe require?
Two fundamentally different ways of measuring the expanding Universe disagree. What's the root cause of this Hubble tension?
How scientists are hearing the gravitational background "hum" of the Universe for the very first time.
Nothing can escape from a black hole. So where do Hawking radiation, relativistic jets, and X-ray emissions around black holes come from?
The concept of the warp drive is currently at odds with everything we know to be true about physics.
For many years, cosmologists have claimed the Universe is 13.8 billion years old. A new paper says no, it's 26.7 billion. How do we decide?
Some 55 million light-years away lies the giant galaxy Messier 87. Its supermassive black hole, inside and out, looks better than ever.
Headlines have blared that quasar ticking confirms that time passed more slowly in the early Universe. That's not how any of this works.
After 15 years of monitoring 68 objects known as millisecond pulsars, we've found the Universe's background gravitational wave signal!
A cute mathematical trick can "rescale" the Universe so that it isn't actually expanding. But can that "trick" survive all our cosmic tests?
In a distant galaxy, a cosmic dance between two supermassive black holes emits periodic flashes of light.
In many ways, we are still novices playing with toy models seeking to understand the stars.
There are 40 billion billion black holes in the universe. Here’s how our Solar System stacks up against ten of them.
When Einstein gave General Relativity to the world, he included an extraneous cosmological constant. How did his 'biggest blunder' occur?
It's been 100 years since we discovered that the Universe was expanding. But if it's expanding, then what is it expanding into?
Einstein's most famous equation is E = mc², which describes the rest mass energy inherent to particles. But motion matters for energy, too.
Before there were planets, stars, and galaxies, before even neutral atoms or stable protons, there was the Big Bang. How did we prove it?
The standard model of cosmology has a big new problem: Some galaxies seem to be too old.
Einstein's relativity overthrew the notion of absolute space and time, replacing them with a spacetime fabric. But is spacetime truly real?
The conservation of energy is one of the most fundamental laws governing our reality. But in the expanding Universe, that's just not true.
All forms of energy affect the expanding Universe. But if matter and radiation slow the expansion down, how does dark energy speed it up?