A physicist answers your questions, and also makes fun of you

Yesterday, I started a facebook thread entitled “Ask Dr. Science.” My friends responded with the nagging questions about the nature of the universe that had been bothering them for a while. Some of my favorites:

Q: Is it true that the Earth will eventually get swallowed into the black hole at the center of the milky way? Does that make you sad?

A: No, but if it were, Yes. The earth’s only got about 5 billion years before the sun turns into a red giant, and even if we had longer, the black hole isn’t the unstoppable killing machine it’s made out to be. After all, it’s only grown to about 3 Million solar masses so far (about a millionth the total mass of the Galaxy). We’re fine.

Q: Why does the moon seem so big in the horizon but so small in the late night sky? I’ve been told the size doesn’t change. Please tell me it’s related to the oceans, as that is a good excuse for changes in size.

A: Rest easy in the knowledge that size doesn’t matter. And it’s not the oceans, either, although it _would_ be cool if the moon got bloated as it submerged. No, the reason the size seems to change is that near the horizon you have something to compare it to, trees and whatnot. Hold your thumb at arm’s length toward the moon when it’s overhead or near the horizon, and it both cases, it’ll approximately span the moon.

Q: Is it possible that the earth is spinning faster making a year seem as though it is much shorter … or is this just part of the aging process for humans? This is a SERIOUS question!

A: As it happens, the tidal forces from the moon cause the moon to slowly increase its orbit and slow down the length of the month. By the same token, the rotation period of the earth is slowing down. This means that the day gets longer, by about 4 milliseconds a century. So… since days are longer, there are fewer of them in a year, but that’s probably not the effect you were thinking of…. Read More

And the grand prize winner:

Q: Can all of Superman’s powers be explained as sub-effects of the singular ability to manipulate the inertia of any matter he comes into contact with?

A: I have to cheat here and expand your question. If we allow superman to (temporarily) change the mass or energy (same thing, of course) of the objects or fields around him, including himself, then we can explain:

Strength: Absolutely

Invulnerability: Yes

Flight: (provided we basically allow him jump and then “swim” through the air) sure — although it’s not clear how he would maneuver in space.

Superspeed: Basically, this is just strength, so yes.

Heat vision: He’d have to do this really fast, but if absorbed visible light photons and reflected them at thermal energies, then sure. Of course, he’d also have to figure a way to increase the intensity of the radiation, or store the light for a long time.

X-ray vision: This is tougher. While he could change visible light to X-rays, it doesn’t do any good to shoot x-rays at people. It’s very bad, actually. X-ray machine work by passing x-rays through something, not by reflecting them.

Super hearing: Presumably if can amplify light-waves, we’ll let him amplify incident sound waves as well.

Freezing breath: One of the cases where he has to remove energy from the system. In this case, we’ve got a super-entropy decrease.

Nothing, however, can explain that ridiculous thing he does in Superman 2 when he throws his “S” emblem at General Zod and his minions.

— If you have your own random physics/astronomy questions, knock yourself out!


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3 Responses to A physicist answers your questions, and also makes fun of you

  1. Henri Salles says:

    I have a double question for a physicist:

    I consider 2 molecules M1 and M2 that have the same mass and same speed (Vstart) in a gas in thermal equilibrium, and that means that their motion coincides to the gas temperature.
    Then I imagine that these 2 molecules collide.
    I understand that the directions of the molecules will very likely be modified.
    As an example a head on collision, modifies only the directions of the 2 molecules but not their speed (Vstart).

    The first part of my question is:
    Can these 2 molecules M1 and M2, after collision, end up having different (than Vstart) speeds V1 and V2?

    The second part of my question is:
    If the answer is yes, supposing that V1 is lower than V2, V2 has then to be greater than Vstart. How can that be? Is there a mathematical demonstration of that? By Boltzmann for instance.

    I cannot understand how the molecules of a gas in equilibrium cannot end up having all the same speed …

    Henri Salles

    • shawn darmody says:

      Great question, I’m am far from a physicist but like you i have always had a facination with reality and its nature.

      when i envision your question I have to convert it to a 2 dimensional frame of reference in this case a table with marbles that represent m1, m2, m3…… if we vibrate the table at a constant oscilation frequency representing the stable energy level of a gas in equilibrium with a constant and equaly consistent amount of energy or force on each marble. I would expect that at a minimum small distances would open up between marbles as they colided into one another that would be analogus to varying acelleration speed of m1 m2 etc.as they continued on their path they would transfer that added speed to surounding marbles either decreasing or increasing their relative speed and altering the direction of force of other molecules or in this case marbles. in the long run the average increases and decreases of speed (or stored potential energy) between the various molecules motion would average out to an energy equal to that imparted by the tables ocilations added to the potential energy stored in the marbles from previous osscilations. so eventhough they have different speeds the overall equilibrium is not lost as the variances cancel each other out.

  2. JeanChauvin says:

    I do not know how to phrase my question. I do not know the language physilish. jHere’s my question.

    Given enough decibals of sound in an isolated tube,could acoustic sound waves create momentum of an object, such as a car or airplane. Which is begging the question, can man create decibals greater then the sound for example a hydrogen bomb and muffle the sound in such a way which causes pressure at the same time

    Is it possible to create a 100 decibals? What would happen assuming there was a way to block the sound from human hearing. What would 1000 decibals do in this situation?

    Also, if you isolate acoustics for the purpose of momentum of a given object, what would happen if you were to add heat with the sound or cold what would happen.

    Dumb question. But given the right circumstances, is it physically possile to drive a car on isolated high decibal sound that is not heard while isolated and muffled out the exhaust. Obviusly 200 Decibals alone can kill a man but this could be addressed.

    But basd on pure sound hypothetically, speaking, say 300 decibals shooting out a tube, would that move a boat, plane? or car?

    If acoustics alone do nothing, is there something you could add with sound to create such an effect, other then magntics, oh vey.

    I await your insults.


    Jean Chauvin

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