Check Out XKCD’s What If?

Relativistic Baseball - What would happen if you tried to hit a baseball pitched at 90% the speed of light?

This looks like something well worth following (and asking questions of!) – go check it out! 

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About Kylie Sturgess

Kylie Sturgess is a Philosophy teacher, media and psychology student, blogger at Patheos and podcaster at Token Skeptic. She has conducted over a hundred interviews including artists, scientists, politicians and activists, worldwide.
She’s the author of the ‘Curiouser and Curiouser‘ column at the Committee for Skeptical Inquiry website and travels internationally lecturing on feminism, skepticism, and science.

  • jamessweet

    So the question immediately comes to mind, how would it be different in deep space? The main problem here is that the ball travelling through the atmosphere is basically creating something sort of like a cross between a gun-type fission bomb and a fusion bomb. What about in a perfect vaccuum? I guess it would be the same, but the boom wouldn’t happen until the batter swung. Or, I guess since the batter is almost certainly going to get a strike here, when the poor catcher is annihilated.

  • Paul Hunter

    So the question immediately comes to mind, how would it be different in deep space?

    Space has diffuse molecules, so the question is, would enough still be in the balls path to cause the same effect?

    • tac

      in deep space, the average density of hydrogen is in the range of a few molecules per cubic meter. You might see a few flashes of light when fusion occurs at the surface of the ball, but wouldn’t have an expanding plasma ball until the baseball strikes the bat.

      A very good example of why everyone wants a rail gun.


    • christophburschka

      I’m not a physicist and can only speculate, but I guess the interstellar hydrogen and stuff is too diffuse to get a chain reaction and an expanding ball of plasma. So the pitcher should be fine (if he’s wearing a space suit I mean), though what happens to the batter is another question (whether or not the bat actually connects).

  • fastlane

    Hah, I love the last bit at the end. Thanks for that.

  • Zinc Avenger (Sarcasm Tags 3.0 Compliant)

    Ah, science.

  • machintelligence

    This also ignores the action-reaction that would hurl the pitcher backwards at a reasonable percentage of the speed of light. But magic was used to accelerate the ball, so it’s O K to ignore it.

  • Robert B.

    Let’s see. The ball has a cross-section of 0.0043 m^2, and it’s 18 meters from mound to plate, so the ball would intersect 0.079 m^3 of space. Interstellar space runs only a few atoms per cubic meters, so there’s actually no guarantee that the space-baseball would hit anything.

    Except the poor catcher. Actually the ball’s not going to have much more trouble going through him than it did going through the air in the atmospheric example, so he won’t get more than a tiny fraction of the kinetic energy and the heat of fusion, but the energy he does get will still blow him apart. Basically, after that “catch” you would be left with two clouds of expanding plasma, one that used to be the ball, headed out of the galaxy at a high fraction of the speed of light, and another that used to be the catcher, trailing behind the ball but mostly concentrated back around the point of impact. I doubt the average velocity of the catcher-cloud would be more than a few hundred meters per second in the direction of the pitch. The batter and pitcher are disintegrated by the blast front of what used to be the catcher, nanoseconds after the impact.

  • snafu

    The energy of a baseball at 0.9c is about equivalent to a 4 megaton nuke. Question is how quickly the air would stop it – if it’s stopped quickly, then it’s equivalent to a bomb, but if it’s stopped gradually, then it’s a fireball moving in a straight line across the landscape.

    A baseball masses 145g and has a cross sectional area of 0.02 square metres. Air at sea level has a typical density of 1.3kg per cubic metre, which is 9 baseball masses. So one baseball mass is one ninth of a cubic metre. One ninth of a cubic metre divided by 0.02 square metres is 5.6 metres. So after the ball has travelled 5.6 metres, we have a combined body of two baseball masses, one baseball mass of ball and one baseball mass of air, with the same total energy as the baseball had by itself a little earlier.

    The air particles may undergo nuclear processes, releasing energetic particles, or they may scatter directly into the environment, carrying away energy that way. Either way, half the kinetic energy of the baseball is diffused into the environment in those first 5.6 metres.

    Realistically, diffusion will be faster than this, since the baseball will not remain the same size – it will disintegrate rapidly. The fireball will expand and thus increase its cross section, sweeping up air more quickly and dumping more energy.

    The end result is that the ball diffuses its kinetic energy in a relatively short distance, and looks pretty much like a largish hydrogen bomb.

    For the space case? The solar wind near Earth has a density of about 7 protons per cubic centimetre. You won’t really notice those interactions. If you miss the ball, you’ll live. If it collides with the bat, then in punching through it will lose enough kinetic energy to reduce you to nuclear vapour.

  • BinJabreel

    So, assuming a total vacuum, and that the ball weighs about .5 kg, it’s relativistic momentum would be over 300,000,000 Newtons, which is roughly enough force to hold up a 300 ton battleship.

    Assuming that the batter has to swing at least as fast as the ball to connect, and that the bat weighs 2.5 kg and is about a meter long… The impulse from them connecting would be something like two or three nuclear bombs worth of force. At least. My crappy phone calculator can’t handle the figures that come back out of these equations. Definitely enough power to damage a small moon.

    • Aliasalpha

      So the rebels should have used baseballs instead of x-wings?

  • jamessweet

    Space has diffuse molecules, so the question is, would enough still be in the balls path to cause the same effect?

    Yeah, that was why I said deep space, thinking there’d be fewer… I’m not actually sure. I doubt it would be enough to cause fusion, but maybe I am wrong. The baseball would definitely get mighty hot though!

  • djp928

    I believe Asimov had a story about a billiard ball being accelerated to light speed in a downtown high rise. In fact, I think the story was called “The Billiard Ball.”

    I don’t recall a horrific explosion, though. Just the ball shooting away at near light speed leaving a neat hole in everything it encountered.

  • gworroll

    It’s pretty clear that the game will end immediately. This would cause equipment failures, which is grounds to suspend a game for later resumption.

    Does MLB have an official offsite, real time record of scores, outs, balls, strikes, and such, so that they could properly resume the game at the appropriate point? Or is this information only officially recorded offsite at the end of the game? How would they handle a resumption if the only official records of game status were destroyed in the event that caused the suspension?

    And what if an entire team is killed in one event? Does MLB provide for the reconstituted team to continue play in the same season, or do they need to wait till the next?

  • Trebuchet

    @BinJabreel: A regulation baseball is 5 to 5-1/4 oz avd, or about .15 kg. The bat is typically a little less than 1 kg. (End of nitpick.)

    I’ve bookmarked “what if” and will be looking forward to Tuesdays now. I wish he had comments/discussion on it. Perhaps on the XKCD message board; guess I’ll have to look.

    • Kylie Sturgess

      I think I’ve discovered that if I have physics questions, my blog comments are the quickest way to get answers!!

    • Binjabreel

      Yeah, I really don’t play baseball. Or pay any attention to it at all, for that matter.