1

Physics, Astronomy & Cosmology / Is it possible to survive a false vaccuum decay?

« on: 08/10/2017 07:25:38 »

Is it possible for humans (current or future) to survive a false vaccuum decay?

For instance, I've wondered if a false vaccuum collapses into a true vaccuum that has only a very, very minute difference in energy level, then perhaps the universe wouldn't change that much, and human life could survive.

2

Physics, Astronomy & Cosmology / How would the universe change if the speed of light increased?

« on: 02/10/2017 01:13:17 »

How would the universe change if the speed of light were suddenly increased, somehow, to a faster speed (for example, 1 trillion times the current speed) ?

Obviously the outer event horizon of the universe would expand and we wouldn't be able to see past events so easily, but I'm curious as to how physical laws might change.

3

Physics, Astronomy & Cosmology / If a brown dwarf gains mass to become a small red dwarf, does the radius alter?

« on: 01/10/2017 11:21:52 »

If a large brown dwarf gains mass and becomes a small red dwarf, does the radius increase, decrease, or remain (roughly) the same?

4

Physics, Astronomy & Cosmology / If the Moon fragmented, could pieces hit the Earth?

« on: 01/10/2017 10:28:46 »

If the orbit of the Moon was for some reason shrunk to the Roche limit of Earth, would the fragments of Moon created be large enough to survive Earth's atmosphere and impact the surface?

5

Physics, Astronomy & Cosmology / What are the implications of cosmic inflation?

« on: 03/07/2017 02:40:09 »

I have a few questions about inflation.

Would the speed of light actually change, and/or would it be observed to change, according to an expanding metric?

In a small universe, we would measure 2 objects to be 1 meter apart, according to our meter-stick, and that light takes a certain time to travel between them.  After the universe expands (and thus our meter-stick expands), we would observe the objects to be 1 meter apart (even though the space between them had actually increased).  But would the length of time for light to travel between the objects change?

Also, back when the universe was small, our 2 objects would feel certain gravitational and electromagnetic forces from each other, based on their distance.  After the universe expands, and our metric also expands, the objects would be observed (using our expanded meter-stick) to have the same distance and volume, even though the distance and volume had actually increased because space expanded.  However, the mass would be the same (I believe).
The formulas for calculating gravity and electric force would predict that the strength of the forces would also remain the same.  Is this true, though?  Would the objects feel the same strength of gravitational pull even though there is more space in between them?

So, here are my root questions:
-- How does the scale of space affect the observed speed of light?
-- How does the scale of space affect forces which influenced by distance?
-- If the speed of light and the forces are observed to be the same before/after expansion, how is it possible to distinguish the scale of space, since the behavior is the same in all scales of reference?

Thanks!

[MOD EDIT - TITLE RE-FORMATTED AS A QUESTION, IN LINE WITH FORUM POLICY]

6

Physics, Astronomy & Cosmology / What are the main sources of electromagnetic radiation?

« on: 22/02/2017 03:34:16 »

For some reason, I can't seem to find much info about this on the internet... at least, not in the form that I'm looking for it.

So far, I've come up with 2 fundamental sources of electromagnetic radiation:

- Spontaneous emission
- Annihilation

There are also things like Thermal Radiation and Gamma Radiation, but it's unclear to me if they are distinct from the above and what the underlying mechanism for them are.
There likely are also other sources that I am missing.

After searching online, every resource that lists sources of electromagnetic radiation seems to list them at the non-fundamental/macro level, e.g. "Lightning" or "The sun"

Can someone help me out here?

7

Physics, Astronomy & Cosmology / Time-dilation effect on rate of event horizon growth?

« on: 31/12/2016 03:39:44 »

We know that events near an event horizon are highly time-dilated to an outside observer. 
Is the expansion of the event horizon itself time-dilated?  (That is, if the black hole quickly gained mass, and the radius of the event horizon expanded rapidly, would an outside observer see the event horizon grow at the same rate as an observer near the horizon?)

Related question: Can the radius of the event horizon grow faster than c?

8

Physics, Astronomy & Cosmology / Can you "ride" a gravitational wave?

« on: 18/12/2016 23:25:34 »

Assume we defined a moving point in spacetime that "rides" a gravitational wave, at the speed of light.  This point would always be between a valley and peak of the amplitude of the wave. 

Would this point experience contracting space in front of it and expanding space behind it?

If so, wouldn't this point experience all of the same effects as a point within the bubble of an Alcubierre drive?

9

Physics, Astronomy & Cosmology / Does Newton's shell theorem account for tidal forces?

« on: 17/12/2016 20:30:50 »

Does Newton's shell theorem account for tidal forces?

If so, wouldn't all spherically symmetric bodies of mass be gravitationally identical to a singularity of the same mass, to an outside observer?

10

Physics, Astronomy & Cosmology / Absolute net velocity of the observable universe

« on: 10/12/2016 00:07:02 »

Let's assume that the entire observable universe was moving through a larger space comprised of vacuum, and that the speed of the observable universe was 0.99 c in some direction. 

According to Galilean invariance, it should be impossible to ever determine whether or not this is true.
Even according to relativity, there would be time dilation, but uniformly throughout the universe, so the speed of the universe could not be detected that way.

But we know that light, no matter the speed of it's source, travels at a constant speed.
This would mean that if I shine a light into my eyes from one direction, it would be red-shifted, and from another direction, it would be blue shifted.  This would allow us to determine our own absolute velocity.
Since we know the velocity of other parts of the universe relative to us, we could then determine the absolute net velocity of the observable universe.

Now, couldn't we use this method to discover our own absolute velocity in real life, and thus the absolute net velocity of the observable universe, however slight it may be?

11

Physics, Astronomy & Cosmology / What limits the angular momentum of a black hole?

« on: 09/12/2016 04:31:28 »

What limits the angular momentum of a black hole?

I've seen articles state that a rotating black hole has a theoretical maximum angular momentum.

Obviously, any object with volume would be limited by the speed of light.  The surface at the equator of a sphere cannot travel faster than light, which limits the spin.

But a black hole is supposed to contain a singularity with no volume.  And the surface of the event horizon isn't a physical phenomenon, so it isn't limited by the speed of light, right?

12

Physics, Astronomy & Cosmology / Why isn't visible light considered ionizing radiation?

« on: 09/12/2016 03:13:30 »

If blue light has enough energy to trigger the photoelectric effect on alkali metals, which frees electrons from the material, that is the very definition of ionizing radiation.
Why isn't visible light considered ionizing radiation?

13

Physics, Astronomy & Cosmology / Does curved spacetime require additional dimensions?

« on: 21/09/2014 09:20:01 »

I always had a bit of difficulty completely grasping the concept of curved space-time. 

To simplify it for myself, I think of a 2-dimentional universe with no time.  Let's say this universe is sphere-shaped.  If I were to plaster this universe onto the surface of a 3-dimentional sphere, it implies that the 3rd dimension must exist for the 2d universe to exist in this shape.

Am I thinking about his in the right manner?  Does this example extrapolate correctly to 4d space-time?  Does our universe require a 5th dimension to be curved?