User pela

104 votes

Simple check for the global shape of the Earth

answered Oct 15, 2018 at 10:53

75 votes

Accepted

What is the speed of sound in space?

thermodynamics astrophysics acoustics plasma-physics interstellar-matter

answered Jan 29, 2015 at 12:59

64 votes

Accepted

Why does moving through time not require energy?

energy spacetime-dimensions

answered Apr 17, 2015 at 9:37

55 votes

Why is the detection of gravitational waves so significant?

general-relativity experimental-physics gravitational-waves ligo

answered Feb 11, 2016 at 15:20

51 votes

Accepted

Can anything be seen from the center of the Boötes void? How dark would it be?

astronomy

answered Apr 17, 2019 at 16:16

32 votes

How to calculate how many photons are in the universe?

homework-and-exercises thermodynamics cosmology thermal-radiation cosmic-microwave-background

answered Aug 28, 2016 at 18:33

30 votes

Why can't I see the blue color scattered by the lower atmosphere of the earth?

visible-light scattering atmospheric-science spectroscopy raman-spectroscopy

answered Nov 17, 2015 at 13:02

29 votes

Accepted

Does the number density of photons $n_\gamma\approx 10^8 \:\mathrm m^{-3}$ refer to CMB photons only?

cosmology astrophysics cosmic-microwave-background baryogenesis leptogenesis

answered Jul 28, 2015 at 9:03

24 votes

Drying clothes with the sun's heat, without any air

thermodynamics vacuum air

answered Apr 7, 2015 at 11:26

23 votes

Accepted

How did the universe shift from "dark matter dominated" to "dark energy dominated"?

cosmology space-expansion dark-matter dark-energy

answered May 23, 2016 at 11:56

20 votes

Accepted

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

thermodynamics temperature thermal-radiation vacuum

answered Mar 31, 2015 at 11:29

12 votes

Why do cosmic rays slow down when passing through the CMB?

cosmology photons cosmic-microwave-background doppler-effect cosmic-rays

answered Jul 4, 2017 at 11:53

10 votes

Accepted

What paper can I cite for the estimated number of atoms in the observable universe to be lower than $10^{82}$?

cosmology resource-recommendations universe atoms estimation

answered Apr 1, 2017 at 15:15

10 votes

Accepted

Results of WMAP mission

cosmology cosmic-microwave-background

answered Oct 1, 2018 at 10:11

10 votes

Accepted

Where is all the Dark Matter? Theoretical Question

astrophysics universe space-expansion big-bang dark-matter

answered Apr 20, 2015 at 9:02

9 votes

Accepted

Is there a delay between force and acceleration?

newtonian-mechanics time

answered May 11, 2015 at 8:54

9 votes

Accepted

How bright was the universe after Big Bang during photon epoch?

visible-light cosmology temperature universe big-bang

answered May 16, 2019 at 10:32

9 votes

Accepted

Is the observable universe equivalent to 'our' light cone?

cosmology speed-of-light astronomy space-expansion relativity

answered Aug 6, 2019 at 12:04

9 votes

Accepted

How can a photon of a particular energy be supplied to a sample of gas to excite the electrons?

quantum-mechanics photons atomic-physics

answered Jun 4, 2021 at 12:01

9 votes

How can IR cameras see things colder than the camera?

thermal-radiation infrared-radiation noise camera

answered Jul 25, 2016 at 6:37

8 votes

Is the light from the Sun the same as the light from a bulb?

visible-light electromagnetic-radiation frequency sun

answered Mar 10, 2017 at 12:16

8 votes

Accepted

Why the CMB has not been dispersed so far?

cosmology radiation space-expansion cosmic-microwave-background blackbody

answered Mar 13, 2015 at 10:27

8 votes

Accepted

Do stray photons become interstellar daggers to a space traveler near the speed of light?

photons space-travel

answered Feb 3, 2016 at 23:38

8 votes

Accepted

What is my real weight?

newtonian-gravity mass weight

answered Feb 4, 2016 at 11:31

7 votes

Accepted

Why can we see the earth from outer space if the sky is blue?

visible-light

answered Nov 3, 2015 at 9:33

7 votes

Accepted

Why don't objects radiate off all of their heat energy?

quantum-mechanics electromagnetic-radiation temperature

answered Nov 13, 2015 at 10:04

7 votes

What is the difference between mean free path and intermolecular distance?

fluid-dynamics terminology kinetic-theory

answered Mar 6, 2017 at 13:42

7 votes

Understanding the units of number density

classical-mechanics dimensional-analysis

answered Jul 6, 2017 at 13:33

7 votes

Accepted

Are galaxies really structured the way they look in pictures?

optics visible-light astrophysics speed-of-light galaxies

answered Sep 7, 2018 at 13:11

7 votes

Will the CMB ever stop shining?

cosmology cosmic-microwave-background observable-universe

answered May 7, 2018 at 13:53

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144 Answers

Simple check for the global shape of the Earth

What is the speed of sound in space?

Why does moving through time not require energy?

Why is the detection of gravitational waves so significant?

Can anything be seen from the center of the Boötes void? How dark would it be?

How to calculate how many photons are in the universe?

Why can't I see the blue color scattered by the lower atmosphere of the earth?

Does the number density of photons $n_\gamma\approx 10^8 \:\mathrm m^{-3}$ refer to CMB photons only?

Drying clothes with the sun's heat, without any air

How did the universe shift from "dark matter dominated" to "dark energy dominated"?

What happens to a body, initially at 300K, kept in isolated space? Will it's temperature drop to 0k?

Why do cosmic rays slow down when passing through the CMB?

What paper can I cite for the estimated number of atoms in the observable universe to be lower than $10^{82}$?

Results of WMAP mission

Where is all the Dark Matter? Theoretical Question

Is there a delay between force and acceleration?

How bright was the universe after Big Bang during photon epoch?

Is the observable universe equivalent to 'our' light cone?

How can a photon of a particular energy be supplied to a sample of gas to excite the electrons?

How can IR cameras see things colder than the camera?

Is the light from the Sun the same as the light from a bulb?

Why the CMB has not been dispersed so far?

Do stray photons become interstellar daggers to a space traveler near the speed of light?

What is my real weight?

Why can we see the earth from outer space if the sky is blue?

Why don't objects radiate off all of their heat energy?

What is the difference between mean free path and intermolecular distance?

Understanding the units of number density

Are galaxies really structured the way they look in pictures?

Will the CMB ever stop shining?