My question is this:
I keep hearing about matter popping into and out of existence in the 'quantum foam' of pure vacuum.
Doesn't that violate the first law of thermodynamics? Matter is energy, so then energy is appearing out of nowhere too.
How do they resolve this?
Thanks...
Well thanks that answered one question. Energy doesn't have to be added to the system for particles to appear.
He didn't get deep into where the particles go when they disappear, other than to imply they annihilate with their birth-twin antiparticle.
I wonder if interstellar and intergalactic space generate new matter as the universe expands. They are the flattest vacuums in nature. If so the universe could expand forever and always have about the same density.
If two particles are born together and space expands between them, I think they would be less likely to find each other again and annihilate. It would create a bias toward creation over destruction. Multiplied by the volume of interstellar space, it would be very common.
I guess a material question is, if the universe is expanding and more space is being made, is vacuum energy diluted, or does its density stay the same?
Space is expanding at large scales. At the scales at which virtual particles pop into and out of existence space isn't expanding significantly...at least not yet. The density of matter in the universe is decreasing
Presuming fusion becomes a reality, would colonization of nearby brown dwarfs make sense? It seems reasonable that at least some should host planetary systems, and a few could lie closer than other, larger stellar bodies.
dailygalaxy.com/2020/09/unexpected-hubble-reveals-something-missing-in-the-dark-universe/amp/
May be a silly question, but I'm wondering how a compass would behave on a massive O'Neill cylinder.
I've read that Mars still has a weak magnetosphere because it has no dynamo (would an O'Neill cylinder have an artificial/simulated dynamo?), and I'm curious if an O'Neill cylinder without a dynamo would be large enough (or whatever) to still have some form of magnetosphere, and how that would likely impact the operation of a compass at various points in the cylinder.
Thanks!
In the video about superconductors, Isaac said something about being able to build much larger structures if you can use superconductors. Does anyone here know how this is possible because it isn't like stress can't transfer the the magnetic fields, Or does it use another property of superconductors?
Superconductors allow you to build buildings that utilize active supports. It not practical now because of energy losses that are an artifact of regular conductors.
A column made from steel and concrete is a static support. Static supports are not the only way to support something off the ground. For instance one can support something with a column of water shot upwards with a water canon. This would be a form of active support. Active supports in real world buildings would use a plasma I imagine.
Isaac's video on Space Towers explains it.
I was looking back on Habitable Planet 2 video and I'm hoping someone can expand (or point me in the right direction) on it.
How can you tell time on a tidally locked planet?
Isaac created an example with a day and night cycle (albeit very long compared to Earth)
But what if it didn't? Are there other ways to tell time since they don't have clear seasonal periods like Earth?
If the planet had a moon you could use its motion in the sky to tell time. Creatures living in the twilight ring where it is not too hot nor too cold would be able to see stars in the sky that would move. Tidally locked planets still rotate, but they do so at a rate that the same side always faces sun.
@RichMigala
So if I'm getting what you're saying right? You're saying a planet can turn on it's y axis instead of X?
Or is it more like a limited rotation, like an eyeball to our sockets and it being only able to do an "O"
Here is a picture that might help. On left the moon rotates so that it is tidally locked. On the right is a moon does not rotate at all. 
On the tidally locked planet the sun stays in the same place in the sky but since it is rotating stars would appear to move. If a being lived on place where starts were visible in the night or twilight sky, the apparent motion of the stars in the sky could be used to tell time.
I'm curious why space tugs aren't being used yet? These devices were first proposed nearly 50 years ago. Now scientists are facing the acute problem of space debris. It would be logical to at least test such devices in real conditions in order to understand what to do with it next.
Does it depend on some kind of regulator?
Or is it just that there are still no effective devices at the moment?
Well, you sort of answered your own question here. No piece of space debris is large enough to warrant a tug being used to pull it, and barring a megastructure that blows up and does not either burn up in the atmosphere or fly out into space, none ever will. But true, we should test a lot more technologies in space. Maybe once launch costs go down....
The only way space tugs will be useful is if we're hauling asteroids to an Earth orbit - but even then, there are alternatives.
I have seen several space tug concept designs that are fairly compact in size. The compact size can greatly reduce startup costs.
In terms of space debris cleaning scientists, 50 objects weighing more than 2 tons are in the first place. It doesn't seem to me that these are too small objects.
I was more interested in the question of regulators.
If such a device can remove large debris from orbit, then it can also remove satellites of other countries. That's what I mean.
Could zeppelins make a come back as mass air travel vehicles?
I've heard the Hindenburg failed because of political pressure to make a propaganda victory which suggests that it's no more sensible to say "zeppelins are a bad idea just look at the Hindenburg" than it is to say "ocean liners are a bad idea just look at the Titanic." Intuitively, it seems like zeppelins should be more efficient than airplanes. Thoughts?
