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Q&A

General Q&A about physics of any type and at any level

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80%
+6 −0
What is inflation in cosmology?

I am having trouble understanding what a cosmic inflation is. Please try to suffice an explanation for non physicists / non formal students for physics / general audience. I understand that an ...

2 answers  ·  posted 5y ago by deleted user  ·  last activity 5y ago by deleted user

inflation cosmology
66%
+2 −0
Should Earth's moon colonies being deep underground ensure natural heating?

Should Earth's moon colonies being deep underground ensure natural heating? By natural I mean "non artificial" i.e. not from "artificial" air conditioning. The question is based on the thought th...

1 answer  ·  posted 5y ago by deleted user  ·  last activity 5y ago by Dave Tweed‭

Moon
40%
+0 −1
decibel level of human hearing(human-auditory-range)

Decibel level listed of solfege. Do Re Mi Fa So La Ti Do 24 27 30 32 36 40 45 80 I saw that whispering decibel level is around 40. And, normal voice level is ...

1 answer  ·  posted 5y ago by deleted user  ·  last activity 5y ago by Olin Lathrop‭

decibel sound wave
71%
+3 −0
Interaction terms in Srednicki's proof of spin-statistics theorem

In Srednicki's proof of the spin-statistics theorem for scalar fields ("Quantum Field Theory", section 4), he considers interaction terms, added to the free Hamiltonian, that are Hermitian function...

1 answer  ·  posted 5y ago by Technically Natural‭  ·  last activity 5y ago by Mithrandir24601‭

quantum-field-theory spin-statistics
40%
+0 −1
Is it rational to freeze water bottles during colder nights, and place them in front of a fan during warmer days?

Is this advice correct? Are they alluding to Freezing Point Depression? Adding salt to tap water lowers the Crystalloid's freezing point. Pour 3 tbsp (51 g) of salt into each of your 3 plast...

1 answer  ·  posted 5y ago by TextKit‭  ·  last activity 5y ago by manassehkatz‭

classical-mechanics
42%
+1 −2
Does folding glasses increase the probability of separating at the hinge?

Please see the images below. I owned these Mykita John glasses for three years, which feels short for glasses to break! Every day, I fold them them before placing it on my night stand and going to ...

1 answer  ·  posted 5y ago by TextKit‭  ·  last activity 5y ago by Olin Lathrop‭

lenses
66%
+4 −1
Why should there not be water below 6kms in the Earths crust?

In 1970, the USSR began drilling at the Kola Super-deep Borehole. The target depth was 15,000 meters; The stated areas of study were the deep structure of the Baltic Shield, seismic discontinuit...

0 answers  ·  posted 5y ago by Conrado‭  ·  edited 5y ago by Conrado‭

pressure
25%
+0 −4
For cleaning food and objects, power scrubber vs. Electric rotary toothbrush? [closed]

I'm not asking about cleaning human organs here. This handheld power scrubber looks like your average rotary toothbrush! Indubitably I know that a toothbrush's brush head can be far gentler than...

0 answers  ·  posted 5y ago by TextKit‭  ·  closed 5y ago by Mithrandir24601‭

pressure
66%
+2 −0
Applying Young-Laplace equation on meniscus formed due to rise of liquid on a single plate

Let's say we have a single plate with liquid on both sides rising up due to surface tension. The meniscus formed has a radius of curvature $R$. I'm trying to find the excess pressure, i.e, the pre...

0 answers  ·  posted 5y ago by TripleFault‭

pressure young-laplace
57%
+2 −1
Why would a 1.74 index lens be more prone to chip and be less resilient than 1.67?

My optician counselled me I don't recommend a 1.74 index with a metal grooved frame, like the one you want from ic! Berlin, because the edge will be less resilient and be more susceptible to chi...

1 answer  ·  posted 5y ago by TextKit‭  ·  last activity 5y ago by Olin Lathrop‭

lenses
40%
+0 −1
Explain like I'm 5 – After glancing at a clock, why does the first second sometimes feel longer than the rest? [closed]

I don't understand either of these Reddit comments that are still too complicated. Please simplify? Alfenhose An interesting phenomena, it is because the brain doesn't store what you saw during ...

0 answers  ·  posted 5y ago by TextKit‭  ·  closed 5y ago by Mithrandir24601‭

time
60%
+4 −2
Would we need Alternating Current if superconducting wires existed?

The major advantage of Alternating Current is that it can be transmitted to large distances without significant losses, which is not possible in Direct Current. Had economical superconducting wire...

2 answers  ·  posted 5y ago by theabbie‭  ·  last activity 5y ago by celtschk‭

superconductor alternating-current
80%
+6 −0
How do constraints work in Lagrangian systems?

I have a question about the discussion of constrained Lagrangian systems in the book Mathematical Aspects of Classical and Celestial Mechanics by Arnold et al. (section 1.2.5). The Lagrangian syst...

1 answer  ·  posted 5y ago by Technically Natural‭  ·  last activity 5y ago by Derek Elkins‭

classical-mechanics lagrangian-formalism constrained-dynamics differential-geometry
80%
+6 −0
How does probability conservation work in Dirac's original formulation of relativistic QM?

I asked this question on Stack Exchange, and didn't get an answer, but maybe someone here will be able to help. In non-relativistic quantum mechanics, the normalization condition for position eige...

1 answer  ·  posted 5y ago by Technically Natural‭  ·  last activity 5y ago by Derek Elkins‭

special-relativity quantum-mechanics hilbert-space dirac-equation normalization
81%
+7 −0
Unusual way to write spacetime coordinates/metric: Is there any downside?

In special relativity, spacetime coordinates are normally given as $$(ct, x, y, z) \tag{S}$$ with the metric being either $$g = \operatorname{diag}(-1,1,1,1) \tag{+}$$ or $$g = \operatorname{d...

1 answer  ·  posted 5y ago by celtschk‭  ·  last activity 5y ago by dmckee‭

special-relativity