User John Doty

30 votes

Time is the only dimension that has an arrow, and the only dimension which contributes an opposite sign to the metric. Is that just a coincidence?

answered May 29 at 12:06

23 votes

If I push someone, what fundamental force do I create?

newtonian-mechanics electromagnetism forces everyday-life interactions

answered Mar 15 at 22:41

22 votes

Why are there three bright spots in the first picture of Sagittarius A*?

general-relativity black-holes astrophysics milky-way

answered May 12 at 16:14

17 votes

Accepted

Failure of Newton's corpuscular theory and success of photon theory of light

electromagnetic-radiation visible-light photons history wave-particle-duality

answered May 16 at 16:40

17 votes

Could the center of the galaxy explode as a result of a chain reaction of stars going supernova?

galaxies supernova structure-formation

answered Apr 13 at 20:42

14 votes

On a magnetar, which force would exert a bigger pull on a 10 kg iron chunk?

gravity magnetic-fields neutron-stars

answered Jul 19 at 22:03

13 votes

How is energy "stored in an electric field"?

electromagnetism energy electric-fields potential-energy capacitance

answered Jun 21 at 13:56

12 votes

How does it make sense for the universe to have started from a big bang?

general-relativity cosmology spacetime big-bang singularities

answered May 14 at 15:22

12 votes

Why do we even need RF cavities to accelerate particles?

electromagnetism radio-frequency particle-accelerators

answered Jul 23 at 11:26

10 votes

Can we get shock by ionic current?

electric-current

answered Aug 1 at 11:41

9 votes

Is it possible to control frequency of the light?

electromagnetism optics electromagnetic-radiation frequency

answered Mar 4 at 13:53

9 votes

What is the connection between mechanics and electrodynamics that makes it necessary for both of these to obey the same principle of relativity?

newtonian-mechanics electromagnetism special-relativity inertial-frames galilean-relativity

answered Jan 17 at 21:50

8 votes

Has anyone charged an object with 1 coulomb? Why was such a ridiculously large charge chosen as the unit of charge?

electrostatics charge history si-units metrology

answered Dec 30, 2021 at 12:36

8 votes

Why didn't the debris collapse back into the Earth at the time of Moon's formation?

angular-momentum conservation-laws collision solar-system moon

answered Jan 23, 2021 at 20:15

8 votes

Why do X-ray telescopes have to be in space?

electromagnetic-radiation atomic-physics material-science atmospheric-science x-rays

answered Aug 20, 2021 at 11:42

8 votes

How did they know the radius of the earth in ancient times?

earth history geometry

answered Apr 9 at 1:32

7 votes

Does thorium-232 emit X-rays?

radiation

answered Apr 23 at 23:48

6 votes

Accepted

Uncertainty Principle in 3 dimensions

quantum-mechanics operators heisenberg-uncertainty-principle commutator observables

answered Mar 29 at 17:26

6 votes

When an electron hits a fluorescent screen mounted on a spring, why can't we get both position and momentum?

quantum-mechanics collision heisenberg-uncertainty-principle spring

answered Jan 5 at 22:28

6 votes

What are some household sources of radiation detectable with a geiger counter?

radiation education home-experiment radioactivity particle-detectors

answered May 17 at 22:32

5 votes

When I drink with a straw, is the atmospheric pressure pushing the water or me sucking it?

fluid-dynamics pressure water

answered Dec 18, 2021 at 0:20

5 votes

How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?

acoustics everyday-life frequency electronics electrical-engineering

answered Mar 4 at 14:05

5 votes

Why do microwaves penetrate flesh when visible light does not at the same intensity?

waves electromagnetic-radiation visible-light microwaves

answered Oct 24, 2021 at 15:22

5 votes

Accepted

Why do photons: "have to give all their energy or none at all", in photon-electron excitation interactions?

quantum-mechanics energy particle-physics photons atomic-physics

answered Apr 19 at 19:14

5 votes

Accepted

A doubt about Kirchhoff's scalar diffraction theory

optics electromagnetic-radiation diffraction

answered Aug 4 at 13:51

5 votes

Is photon path pre-defined at the time of emission?

special-relativity photons quantum-electrodynamics observers determinism

answered Jul 23 at 15:50

5 votes

Is it "mathematically wrong" to ignore dual spaces, 1-forms, and covariant/contravariant indices in classical mechanics?

classical-mechanics differential-geometry metric-tensor coordinate-systems covariance

answered Jul 11 at 18:37

4 votes

How can the given formula yield a frequency, when it doesn't have a parameter with time units?

electromagnetism frequency

answered Jul 12 at 13:41

4 votes

Why Doesn't the Stefan-Bolzmann Law Deter Controlled Fusion Engineers From Seeking Extreme Temperatures To Maximize the $nτT$ Triple Product?

temperature nuclear-physics thermal-radiation fusion

answered Jul 29 at 17:06

4 votes

Gravitational waves on rigid bodies

general-relativity spacetime gravitational-waves ligo

answered Oct 31, 2021 at 20:53

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182 Answers

Time is the only dimension that has an arrow, and the only dimension which contributes an opposite sign to the metric. Is that just a coincidence?

If I push someone, what fundamental force do I create?

Why are there three bright spots in the first picture of Sagittarius A*?

Failure of Newton's corpuscular theory and success of photon theory of light

Could the center of the galaxy explode as a result of a chain reaction of stars going supernova?

On a magnetar, which force would exert a bigger pull on a 10 kg iron chunk?

How is energy "stored in an electric field"?

How does it make sense for the universe to have started from a big bang?

Why do we even need RF cavities to accelerate particles?

Can we get shock by ionic current?

Is it possible to control frequency of the light?

What is the connection between mechanics and electrodynamics that makes it necessary for both of these to obey the same principle of relativity?

Has anyone charged an object with 1 coulomb? Why was such a ridiculously large charge chosen as the unit of charge?

Why didn't the debris collapse back into the Earth at the time of Moon's formation?

Why do X-ray telescopes have to be in space?

How did they know the radius of the earth in ancient times?

Does thorium-232 emit X-rays?

Uncertainty Principle in 3 dimensions

When an electron hits a fluorescent screen mounted on a spring, why can't we get both position and momentum?

What are some household sources of radiation detectable with a geiger counter?

When I drink with a straw, is the atmospheric pressure pushing the water or me sucking it?

How do headphones and earphones produce good bass if tiny speakers can't produce low frequency sounds very well?

Why do microwaves penetrate flesh when visible light does not at the same intensity?

Why do photons: "have to give all their energy or none at all", in photon-electron excitation interactions?

A doubt about Kirchhoff's scalar diffraction theory

Is photon path pre-defined at the time of emission?

Is it "mathematically wrong" to ignore dual spaces, 1-forms, and covariant/contravariant indices in classical mechanics?

How can the given formula yield a frequency, when it doesn't have a parameter with time units?

Why Doesn't the Stefan-Bolzmann Law Deter Controlled Fusion Engineers From Seeking Extreme Temperatures To Maximize the $nτT$ Triple Product?

Gravitational waves on rigid bodies