## Top new questions this week:

### Do all the conservation laws of Physics take no time to propagate?

For instance, conservation of momentum, does it take time to propagate between two or more objects? If it does, then there would be some moment that the momentum is not conserved. If it doesn't take ...

conservation-laws faster-than-light

### Are Hubble Telescope Images in true color?

Like many others, I have marveled at the images made available from the Hubble Space Telescope over the years. But, I have always had a curiosity about the color shown in these images. An example is ...

astronomy telescopes

### What is the smallest distance possible between two stars?

If two stars of any type were to form near each other, how closely can they form before something prevents them from being two distinct stars?

stars

### Conical train wheels

I've been reading about how the conical shape of train wheels helps trains round turns without a differential. For those who are unfamiliar with the idea, the conical shape allows the wheels to shift ...

homework-and-exercises newtonian-mechanics friction rotational-kinematics free-body-diagram

### Is an electron a superconductor?

A superconductor has zero resistance. What about an electron in a vacuum? Could this simple system be considered superconducting?

superconductivity

### Earth still exists - does this fact tell us anything about LHC safety?

When LHC was about to be launched there were many fears that it would destroy the world. To counter them scientists tried to carefully examine all possibilities and concluded that there is nothing ...

### Can two colliding photons create a Higgs Boson?

The LHC discovered the Higgs using the following decay mode: $$H^0 \rightarrow \gamma \gamma$$ This got me thinking: if we reverse this mode, will it be valid? In some annihilation/decay pairs, ...

particle-physics photons standard-model higgs

## Greatest hits from previous weeks:

### Relation between pressure, velocity and area

In a nozzle, the exit velocity increases as per continuity equation $Av=const$ as given by Bernoulli equation (incompressible fluid). Pressure is inversely proportional to velocity, so we have lower ...

fluid-dynamics aerodynamics

### Does gravity exist in a vacuum?

My understanding has always been that it does from conventional science courses, but really thinking about it, I was wondering if this is really the case. To my limited understanding there is a ...

quantum-gravity vacuum

### Is it degeneracy pressure rather than electrostatic repulsion that stops us falling through the floor?

From Wikipedia: Degeneracy Pressure Freeman Dyson showed that the imperviousness of solid matter is due to quantum degeneracy pressure rather than electrostatic repulsion as had been previously ...

electromagnetism atomic-physics pauli-exclusion-principle

### General proof of formulas of geometric optics?

In most lf textbooks formulas of geometric optics like lens maker formula and base formula for that are proven (or rather verified from my point of view) by taking specific case (ray diagram) and ...

optics conventions geometric-optics lenses