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12 votes
Accepted

Does the existence of hydrogen in the universe create an obscuration effect similar to the way air does at great distances?

One way of thinking about this is in terms of the physics of the cosmic microwave background. The cosmic microwave background occurs as a phenomenon when a nearly homogeneous universe transitions ...
ProfRob's user avatar
  • 155k
11 votes

How does the Earth not lose its atmosphere to space?

Your assertion that our atmosphere doesn't escape is wrong. Helium and Hydrogen atoms have a low enough mass that they do have an escape velocity at the temperatures on the edge of our atmosphere. ...
UKMonkey's user avatar
  • 211
9 votes

How does the Earth not lose its atmosphere to space?

The underlying reason that the molecules of Earth's atmosphere do not fly away into the surrounding vacuum is that they are slower than the escape velocity, which would be 11200 m/s. The typical ...
Peter - Reinstate Monica's user avatar
6 votes

Why does radiation not need a medium to travel?

Electric and magnetic fields can and do exist in a vacuum. Electromagnetic waves are just fluctuations in electric and magnetic fields. In a vacuum (meaning no charges or currents, which do require ...
ProfRob's user avatar
  • 155k
6 votes

How does the Earth not lose its atmosphere to space?

update: This answer was written before the question was modified. I've tried to explain where a value like 10-17 Torr for deep space might come from, but it's since been dropped in lieu of 10-11 Torr ...
uhoh's user avatar
  • 31.1k
6 votes

Does the existence of hydrogen in the universe create an obscuration effect similar to the way air does at great distances?

In a sense yes - there is interstellar (i.e. intra-galactic) absorption of Lyman-$\alpha$ photons by neutral hydrogen. This plays a role e.g. when trying to determine how much hydrogen is lost from ...
AtmosphericPrisonEscape's user avatar
5 votes

How does the Earth not lose its atmosphere to space?

Space is low pressure and the earth’s atmosphere is high pressure. In order to have any pressure the gas requires (demands) that it press upon something. Yes, and that 'something' is Earth's gravity....
Hobbes's user avatar
  • 3,034
3 votes

Could vacuum energy dim standard candles?

Locally, energy and momentum must be conserved. So no, a photon cannot lose energy or change momentum by interacting with virtual particle pairs that have a net energy and momentum of zero.
ProfRob's user avatar
  • 155k
3 votes

How do we know that vacuum is devoid of matter?

What "vacuum" means depends on who you ask: If you ask a general relativist, they will tell you that a region of space-time is a vacuum if the right-hand side of the Einstein Field Equations is zero. ...
Steve Linton's user avatar
  • 10.3k
2 votes

How do we know that vacuum is devoid of matter?

You are misquoting and perhaps misreading A "vacuum is space devoid of matter". This is the definition at the top of the page. It then goes on to note that true vacuums don't exist, but ...
James K's user avatar
  • 124k
2 votes

How do we know that vacuum is devoid of matter?

This is just the definition of vacuum. A vacuum is a space from which everything that we know can be removed has been removed. It still has dark energy and the Higgs field and spacetime geometry in ...
benrg's user avatar
  • 3,860
2 votes

How Essential is the Vacuum Energy to Our Present Model of the Expanding Universe?

I'm neither a quantum physicist, nor a cosmologist, so I'm going only from my laymans understanding. The framework for constructing theories to explain everything in the universe except gravity ...
Steve Linton's user avatar
  • 10.3k
2 votes

How does the Earth not lose its atmosphere to space?

I think uhoh covered proximity but just to induce equilibrium to further elaborate: First of all, positive pressure and negative pressure are just terminology based on where we started i.e. 1 atm and ...
HR04375439's user avatar
2 votes
Accepted

What would happen if you jumped out of a moving spacecraft?

If the spacecraft is not accelerating, the astronaut leaves the airlock and just floats outside, not moving relative to it. If the rocket is accelerating they "fall" down towards the stern from the ...
Anders Sandberg's user avatar
1 vote

Are vacuum fluctuations that produce dark matter correlated to fluctuations that produce baryonic matter?

Yes. This question was only settled in the last decade or so, but initial variations in the baryon density and in the dark matter density seem to agree at the percent level. See for example "...
Sten's user avatar
  • 4,753
1 vote

Why does radiation not need a medium to travel?

It's an interesting question which can get you quickly into deep physics. The simple way to view it is the light being made up of photons, which can be viewed and act as particles. Then, when the ...
radu_cloud's user avatar

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