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Within our observable Universe, there’s only one Earth and one “you.” But in a vast multiverse, so much more becomes possible.

Some constants, like the speed of light, exist with no underlying explanation. How many “fundamental constants” does our Universe require?

The information we have in the Universe is finite and limited, but our curiosity and wonder is forever insatiable. And always will be.

Signals from across the universe point toward a fascinating possibility.

Does it have a deeper significance — or is it just a number?

There are some 26 fundamental constants in nature, and their values enable our Universe to exist as it does. But where do they come from?

There are limits to where physics makes meaningful predictions: beyond the Planck length, time, or energy. Here’s why we can’t go further.

One of the fundamental constants of nature, the fine-structure constant, determines so much about our Universe. Here’s why it matters.

In the year 2000, physicists created a list of the ten most important unsolved problems in their field. 25 years later, here’s where we are.

A few physical quantities, in all laboratory experiments, are always conserved: including energy. But for the entire Universe? Not so much.

Two of the answers add a dimension to physics that doesn’t belong there. Maybe we could call it “astrotheology.”

Perhaps the most well-known equation in all of physics is Einstein’s E = mc². Does mass or energy increase, then, near the speed of light?

Empty space itself, the quantum vacuum, could be in either a true, stable state or a false, unstable state. Our fate depends on the answer.

The original principle of relativity, proposed by Galileo way back in the early 1600s, remains true in its unchanged form even today.

Einstein’s general relativity has reigned supreme as our theory of gravity for over a century. Could we reduce it back down to Newton’s law?

The fact that our Universe’s expansion is accelerating implies that dark energy exists. But could it be even weirder than we’ve imagined?

DESI, by mapping galaxies, has claimed they see evidence for dark energy evolving by getting weaker. But that’s only one interpretation.

Different methods of measuring the Universe’s expansion rate yield high-precision, incompatible answers. But is the problem robustly real?

Humans, when we consider space travel, recognize the need for gravity. Without our planet, is artificial or antigravity even possible?

The Universe is expanding, and the Hubble constant tells us how fast. But how can it be a constant if the expansion is accelerating?

It’s possible to remove all forms of matter, radiation, and curvature from space. When you do, dark energy still remains. Is this mandatory?

Holograms preserve all of an object’s 3D information, but on a 2D surface. Could the holographic Universe idea lead us to higher dimensions?

Measurements of the acceleration of the universe don’t agree, stumping physicists working to understand the cosmic past and future. A new proposal seeks to better align these estimates — and is likely testable.

There was a lot of hype and a lot of nonsense, but also some profoundly major advances. Here are the biggest ones you may have missed.

For nearly 25 years, we thought we knew how the Universe would end. Now, new measurements point to a profoundly different conclusion.

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.

Most fundamental constants could be a little larger or smaller, and our Universe would still be similar. But not the mass of the electron.

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?

Is gravity weaker over distances of billions of light-years?

A cute mathematical trick can “rescale” the Universe so that it isn’t actually expanding. But can that “trick” survive all our cosmic tests?