(Phys.org)—One of the first observations suggesting the existence of an invisible dark matter came in 1933 when astronomer Fritz Zwicky noticed that galaxy clusters were more energetic than they ...

The equivalence principle is one of the more fascinating ideas in modern science. It asserts that gravitational mass and inertial mass are identical. Einstein put it like this: the gravitational force ...

Physicists report that electrons in semiconductor crystals have a negative inertial mass when strongly accelerated in an electric field. Physicists of the Max Born Institute in Berlin report in the ...

We're only going to deal with one dimension here so we'll neglect the vector nature of the force. Let's consider a force, $F$, which increases linearly with ...

I've been trying to explain quantum physics, forces, relativity, and space-time to my kid and we had a question that I'm finding difficult to find a solid answer to. Background you can skip if you ...

At the heart of Einstein’s theory of gravity (general relativity) is the equivalence principle. The equivalence principle says that there is no difference between being stationary and subject to ...

Antimatter is anti- a lot of things, but it’s not supposed to be antigravity. An antimatter particle does have the opposite electric charge of its ordinary matter counterpart. But the mass of both ...