• June 12, 2020, 7:37 a.m.
  • June 28, 2020, 11:52 p.m.

    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?


  • June 29, 2020, 8:47 a.m.

    This should answer your question.

  • June 29, 2020, 10:53 p.m.

    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?

  • June 30, 2020, 6:03 a.m.

    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

  • Sept. 13, 2020, 11:41 a.m.
  • Oct. 27, 2020, 10:19 p.m.

    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.


  • Oct. 30, 2020, 9:42 a.m.

    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?

  • Oct. 30, 2020, 7:13 p.m.

    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.

  • Nov. 15, 2020, 9:54 p.m.

    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?

  • Nov. 24, 2020, 6:54 a.m.

    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.

  • Jan. 22, 2021, 1:07 a.m.

    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"

  • Jan. 22, 2021, 9:19 p.m.

    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.

  • Feb. 10, 2021, 3:01 p.m.

    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?

  • Feb. 11, 2021, 8:09 a.m.

    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.

  • Feb. 11, 2021, 1:13 p.m.

    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.

  • March 18, 2021, 7:23 a.m.

    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?

  • June 15, 2021, 4:41 p.m.

    I've discovered only recently this series, and I'm watching it from the start bit by bit.
    But when I arrived to the Matrioshka world episode, there was a point that sound strange to me: IA start talking about how to increase the radiating surface of the Matrioshka world to help with heat management, but even if my physics is a bit rusty, it seems to me that in vacuum, where there is no convection, only radiation is useful, and for this reason only the part of an hypothetical fin that's invisible to any other fin would be useful, otherwise they would simply be radiating heat into each other.
    So, creating complex fractal figures to radiate heat would not be really useful, as the best way should be simply having the largest flat surface perpendicular to the radiating light of the sun... or am i missing something?

  • July 10, 2021, 7:41 a.m.

    What's the name of the idea or hypothesis that says that the new aliens we will encounter will have a physical appearance closer to us, with two eyes, with limbs... etc
    since we are probably in the mean average of how things look like.

    Meaning the first alien we encounter will probably have a fair resemblance to us —maybe it looks like an insect— but it wont be a gaslike being with no internal organs since that would drift so much apart from us.

  • July 11, 2021, 6:08 a.m.

    You could be talking about a couple of different things. First there is the Principle of Mediocrity. Below is Wikipedia's definition:

    You could be talking about Convergent Evolution. Again Wikipedia:

    I think the general consensus is that if we ever run into intelligent aliens they won't remotely resemble us. While I don't believe they will look like star trek aliens(just like us but with prosthetic foreheads on their real foreheads), I am sure we will share a lot of same form and features. Bilateral symmetry, two forward facing eyes, opposable digits, etc.

  • July 12, 2021, 11:18 a.m.

    Thank you

  • July 14, 2021, 5:56 a.m.

    Below is an example of convergent evolution. It depicts a Thylacine and Wolf. Two completely different species. The last common ancestor between these two species was a shrew like animal about the size of your thumb that lived 160 million years ago. If you came across one their skulls, you'd need to be an expert to know which one was which. The two species evolved isolated from each other on different continents; the Thylacine is from Australia and the Gray Wolf is from where ever gray wolves came from.

    What can we conclude this example? Life favors certain shapes for certain niches. If we ever find the skull of an intelligent alien species, it might be eerily similar to a human skull....so much so that who ever finds might mistake it for a human skull.

    Convergent evolution

  • Sept. 23, 2021, 11:04 p.m.

    Since I started watching Science & Futurism on nebula, there were a lot of times when further questions popped into my head. So I thought I'd try posing one here. So here goes the first post:

    So habitats beeing also spaceships and some could have an outer athmosphere e.g. hydrogen as shielding - what happens when parts of this gas get ionized ( e.g. cosmic or other radiation) and the habitat and thus the gas accelerates? An accelerated charged particle should emit light, but then again it is only accelerated seen from the outside. The gas shouldnt move (much) in relation to the habitat. So would it only emit photons away from the habitat? head scratch

    Perhaps someone can lift my confusion. ^^ regards pyriel