Posts Tagged ‘Einstein’

Special Relativity for Dummies, I mean writers

So, practically everyone knows thanks to Albert Einstein that on a starship traveling close to the speed of light time will pass more slowly than in the rest of the universe, though it does seem that not everyone understands how that works.  For example, I recall reading a passage in The Andalite Chronicles where the narrator explained that they were traveling to earth at a sub-light speed that would take them about three days because if they went at maximum burn they might make it in a few hours but that would be years on earth.  That’s just wrong, relativity slows down time onboard the ship, it doesn’t speed up time outside or anything.
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Entering the Unknown (Or, What Happens When Timmy Falls Down a Black Hole)

When I think about black holes in science fiction, I can’t help but think of that old Disney movie The Black Hole.  I was five years old (or maybe seven) when I saw it, so all I really remember is an uneasy glance passing between two astronauts as their space shuttle hurtles into a black hole.  At the time, this was scary – hey, I was five (or seven).  But it could have been so much scarier.

Black Hole

Since that movie came out in 1979, public perception of black holes has changed a bit.  The director of a Hollywood remake might be aware that astronauts can’t just fly calmly, or anxiously for that matter, into the very center of a black hole.  Strong gravity would pull an astronaut apart as they approach the singularity, starting with the nearest body part.  Let’s say an astronaut, we’ll call him Timmy, falls into a black hole feet first.  His feet will stretch toward the singularity.  His head will stretch too, but by a lesser amount.  He might even have a moment or two to examine the lengthening of his body before he is stretched into a thin strip of spaghetti and slurped into the singularity.  There is a technical term for Timmy’s experience: spaghettification.


Spaghettification is a better explanation than what Disney came up with, but it doesn’t tell quite the whole story.  It’s true that once inside a black hole, Timmy would stretch tidally toward the singularity.  But as Timmy becomes taller and skinnier, the curvature of space itself changes.  The stretching quickly becomes so extreme, it produces its own gravitational field.  Turns out, gravity as Einstein thought of it is not the gravity we know and love.  Near something as extreme as a singularity, gravity becomes non-linear, meaning that gravity begets gravity.  So once Timmy starts stretching, all bets are off – as soon as he stretches one way, he induces an extreme curvature of space that reverses the stretch.  The oscillations will speed up as Timmy approaches the singularity, kneading him like dough one way then the other.  Theorists, not without a sense of humor, call this “Mixmaster dynamics,” named after the dough-kneading machine.  (By the way, in the simulation below, the blob stretches by a factor of 6.  Timmy, however, would stretch by a factor of 10^14.  For those not inclined to scientific notation, that’s a one followed by 14 zeroes…in other words, many times more than my measly brain can imagine.)

Mixmaster dynamics

Gravity begets gravity, and so the bread-making begins.

Lucky for Timmy, the mixing doesn’t last long.  As soon as Timmy enters the singularity, he ceases to exist, his mass and energy converted to the energy of the black hole’s gravitational field.  At the singularity, matter no longer matters.  We might think of black holes as gaining mass as they swallow gas, stars, and little boys and their dogs, but really there is no mass at all, just a self-generating gravitational field.

Of course, the story for Timmy could end differently.  Einstein’s General Theory of Relativity describes gravity, but is limited to the world of Big Things.  Small Things, like atoms and electrons, are governed instead by quantum mechanics.  Singularities, being very small objects with extreme gravity, must be governed by both, but theorists have yet to understand how these two vastly different ideas might mesh together.  I bet Timmy can’t wait to find out.