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Physics, Astronomy & Cosmology / Re: If atoms are mostly empty space, why is the Earth not transparent?

« on: 25/12/2017 03:09:28 »

Well it's a bit more complicated than you're thinking it is.

First, light is energy, and massless. But according to E=mc^2 energy is mass. So a photon of light with specific energy does have a relativistic mass. But that's not really important here.

Second, light doesn't pass through everything, it gets absorbed.

Sure materials would be "relatively" transparent if they were a single atom layer thick, but they're not. A piece of paper is several hundred thousand layers thick. These atom layers are bound together in a lattice like a crystal. How tightly compacted the layers are is dependant on the size of the atoms and the charges binding them. Then you need to consider that an electron isn't a distinct solid particle orbiting the atom like a planet around the sun. An electron is more of a cloud of charge with the "particle" existing somewhere in that cloud basically jumping around blinking in and out of existance.

So now a piece of paper, hundreds of thousands of atoms thick, each atom has electrons. Hydrogen has 1. Carbon has 6. Oxygen has 8. So hundreds of thousands of atom nuclei and millions of electrons. That's just in thickness at any point.

Now consider that a photon acts as a wave, so it doesn't just travel in a straight line. It oscellates up and down as it moves forward. So imagine a material an inch thick. If it travelled straight through it's distance travelled in the material would be an inch. But it's not travelling straight through it's moving up and down so the distance travelled would be greater than an inch.

All of this drastically increases the likelihood of an interaction occurring between the photon and some part of an atom causing the photon to be absorbed and decreasing the number that passes through.

Smaller wavelength photons such as gammas, are so small they can basically drill their way through without being absorbed, appearing to travel in a straight line because their oscillation is so small. Whereas larger wavelength photons, like am radio, are so large that when passing through materials they actually do travel in a straight line and can make it without being absorbed. Which is why am radio is so reliable.

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General Science / Re: If Humans Were Wiped Out Would The World Survive ? (A nuclear power question)

« on: 13/12/2017 05:10:26 »

Nuclear reactors have many fail safes. If anything goes wrong then control rods immediately drop into place and shut down the reactor. Eventually the water would probably boil away causing a meltdown or hydrogen gas would build up causing an explosion and radioactive material would spew out. The immediate area would probably be pretty bad but radiation damage is nothing compared to all of the massive damage we inflict on the planet every day. Burning fossil fuels, deforesting, dumping trash, plastic everywhere, chemicals everywhere, overhanging and overfishing. Things would probably get bad for a while, maybe a couple thousand years. But that amount of time is a drop in the bucket in geological terms.

That's why when people say "we need to stop killing the planet" I say "No, the planet will be just fine, we need to stop killing ourselves."

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Question of the Week / Re: QotW - 17.12.10 - Do fish yawn?

« on: 13/12/2017 04:55:36 »

I'm no fish expert but from what I understand the breathing process in mammals requires the swapping of carbon dioxide with oxygen. This relies on a careful balance between the two. When you aren't getting enough oxygen and there is a build up of carbon dioxide then a yawn is triggered causing you to breathe in deeply, restoring the balance.

In a fish this gas exchange takes place in the gills as water passes through them. Because of this, fish don't have to breathe like we do and therefore don't yawn.

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General Science / Re: How many people can the Earth support sustainably?

« on: 24/11/2017 05:30:18 »

I read a report on the topic once that said the limit is about 10 billion.

Food isnt really an issue. The US alone has the growing capacity to sustain much of the human population. The issue with food is getting it to people who need it. Half goes from field to trash without ever making it to a kitchen.

The limiting factor they concluded was access to fresh water. There is only so much fresh water on the planet to sustain so many people. We can desalinate ocean water but the weather system and rivers dump freshwater right back into the oceans. So there is a limit. And we're pretty much at that limit.