Comments on: xkcd is so much better than I could have imagined

By: Amanda

Amanda — Wed, 17 Nov 2010 18:08:51 +0000

Why is the velocity low at small distances? I get the flattened part and why but am i right in thinking that the velocity increases with distance for the inner, visible part of the rotation?????????//

By: Vicky Ge

Vicky Ge — Thu, 11 Feb 2010 19:11:49 +0000

I will make this the viable alternative to HarvardFML.

By: rachel

rachel — Mon, 14 Dec 2009 02:47:04 +0000

One neat thing about ocean-floor life is that some animals near hydrothermal vents don’t have mouths. They don’t eat, but they have gills that take up nutrients from the volcanic vents (like hydrogen sulfide–yum yum). Instead, they’ve got these colonies of chemoautotrophic bacteria that live inside of them and use these really poisonous compounds to produce energy and the synthesis of carbohydrates for the animal. It totally redefined the way that we think about life existing in places without sunlight.

There’s also the fun feature of deep-sea gigantism, where normal-looking creatures grow to enormous sizes, when they’re much smaller in other places. For example, our TFs brought in an isopod (think roly-poly or pillbug) from the deep sea–except it was the size of my head. I got to hold it, dead and frozen of course, but still neat.

But I digress. And ought to be studying. Wooo–so close to being done!

By: tom

tom — Sun, 13 Dec 2009 06:03:52 +0000

So it turns out that if you have some dynamic system of gravitationally interacting bodies (like a cluster of galaxies, or even a cluster of stars), the kinetic energy of the system (which is dependent on the velocities of stuff) is related to the gravitational potential energy of the system (which is dependent on the masses and distances between the stuff) via the “Virial theorem” (http://en.wikipedia.org/wiki/Virial_theorem). So, if you see a cluster of galaxies and get a sampling of their velocities, you can transform them into kinetic energies, use the Virial theorem to see how much gravitational pull there is, and get a mass of the system of it. Which might be a lot more than if you just added the masses of the individual galaxies together (even accounting for dark matter inside each galaxy)!

Also, sometimes this happens: http://en.wikipedia.org/wiki/Bullet_Cluster

Hey, you should tell us some cool things about ocean-floor life.

By: rachel

rachel — Sun, 13 Dec 2009 04:29:59 +0000

You’re giving me so many interesting things to read about when I should be reading about the biology at the bottom of the ocean. Dang it.

How do people know there’s too much mass–or dark matter, I guess, is what you’re implying (correct me if I’m wrong)–between galaxies when those areas aren’t rotating? Or are they? I was also looking at the wikipedia page on gravitational lenses. They look pretty neat.

By: duncan

duncan — Sat, 12 Dec 2009 22:12:43 +0000

On Man Day, I ran up the escalator at Alewife and bloodied myself up pretty well. Good decision.

They often find too much mass not only inside galaxies but also between galaxies, when you look at galaxy clusters, and also sometimes there are dark objects that act as gravitational lenses when we look at distant objects. If you would like a lecture on dark matter, this would be a great week to ask, because I’ll be spending all week studying for my astronomy final.

By: rachel

rachel — Sat, 12 Dec 2009 21:58:23 +0000

Conclusion: escalators are actually made of dark matter. Or maybe adulthood is. They tell me I’m supposed to feel like a grown-up, but it’s not happening yet.

This is seriously interesting, though–I didn’t know the reasoning behind the theory for dark matter. I’m not sure I know enough about the physics to make a strong case for or against this, but the general concept of it is fascinating.

By: Martin Ye

Martin Ye — Fri, 11 Dec 2009 15:40:46 +0000