Friday, July 12, 2013

The Colours of Space (and Currents)

I recently read (well, listened to) The Colours of Space by Marion Zimmer Bradley. You can read my proper review over at my book blog,  but here I wanted to discuss some of the science that popped up in the book.

The title of the novel — The Colours of Space — refers to the stars being much more brightly coloured when seen in space, as compared with when seen from inside the Earth's atmosphere. (There's another reference there to plot elements as well, which I won't spoil, but I read the main reference as being to the multi-coloured stars.) The thing is, the phenomenon, as described in the story, is not entirely real. Yes, stars come in different colours, but those colours range from red to yellow, white and blue. There are no green stars. 

Interestingly enough, this isn't the first time I've encountered the idea of green stars in old science fiction. I understand where the misconception comes from — wanting to move through the optical spectrum with increasing temperature — but that's not quite how it works. Have you ever seen something glow "green-hot"? No. That's because green is in the middle of the visible spectrum and when it's the peak wavelength of a black body, the object is still emitting strongly in the neighbouring red and blue wavelengths which, when they're all combined, appear white. Similarly, blue stars (and red stars) aren't blue like the sky; they look pretty white because the star is still emitting strongly in the other visible wavelengths.

The Orion Nebula. Image credit: NASA/ESA
On the other hand, it's not unreasonable to think that Earth's atmosphere would bleach out the "real" colours of objects in space. After all, hills and whatnot in the distance often look paler than up close (because of water and often pollution in the atmosphere). But we can still see distinct colours of stars even from Earth and even, if you have binoculars or a good camera, the colours of nebulae (which are entirely prettier than mere stars). The constellation of Orion is a good example. Betelgeuse is a red giant (down the bottom of Orion if you're in the Good Southern Hemisphere), the Orion Nebula looks purplish (on the "handle" of the bit that looks like a saucepan from the south), the Horsehead Nebula (in Orion's Belt) is on the pink side, and the rest of the stars are yellow, white and blue but all look fairly white (from Earth AND space).

This reminds of another old book in which the underlying premise is based on now-outdated and hilariously erroneous science: The Currents of Space by Isaac Asimov. In that book a rather important plot element is that supernovae are caused by clouds of gas (the titular currents) drifting around space and every now and then changing the elemental makeup of stars enough to make them explode. (I think specifically it was clouds of carbon, but I don't have the book nearby to check.) We now know that this is mostly nothing like what causes supernovae.

There are two types of supernovae: core-collapse and Type Ia. Core-collapse supernovae occur when a massive star (more than around ten times the mass of our sun) runs out of fuel in its core and can no longer maintain its size and collapses in on itself and explodes. To put it very simply. Type Ia supernovae occur when a white dwarf (the corpse of a star originally like our sun) has another star nearby feeding it matter. When the white dwarf gets too massive to maintain its fundamental (proton and electron) structure, it will collapse in on itself and explode (and become a neutron star).

Just because these books are based on science we now know not to be true, doesn't mean they're not worth reading (although I suspect it contributes to them being out of print). Have you read any other books with science that was reasonable when they were written, but doesn't stand up to the test of time and progress?

Sunday, April 28, 2013

Friction in space and on Earth

This post is in response to a comment I got on my previous post "More thoughts on the importance of science in science fiction" where Shannon commented/asked (I'm only quoting the question-y part of her comment):
It really is a hard concept to grasp, the no-friction-in-space thing. I don't think I really get it - I'm not sure how to visualise it, for a start - but I don't understand how a space ship - of the super-advanced, sci-fi kind - can't slow down. I mean, it's mechanical and computerised and runs on fuel; on Earth anything we build for transportation will slow down especially if there's a mechanical failure etc. I know in space you can't "stop", you'd only drift, right? I'm hoping you can explain this a bit more to me because I really do want to understand!

(The more time I have to let this concept dwell in my brain, the more I'm starting to get it. So what does happen when you, in sci-fi, go from "warp speed" or whatever they like to call it, to, well, not?)

On Earth (or really, anywhere that isn't the empty vacuum of space) moving objects slow down because they lose energy through friction — rubbing against other objects. Commonly on Earth, the source of friction would be land, water and/or air.

Some examples:
  • The motor of a boat needs to stay on to keep the boat moving, because if the motor is turned off, the boat will be slowed down by the water pushing back against it.
  • If you ski straight down a hill (let's say a small hill for safety reasons) you will accelerate (get faster) while you're going down hill, but once you reach the flat bit at the bottom you will eventually slow down and stop without having to stop yourself. This is because of the friction between the snow and your skis. Generally, skiing works because there's much less friction between snow and skis than, say, between shoes and dirt, but there isn't zero friction. When you were going down the hill and getting faster, there was still friction, but at that point gravity pulling you downwards was stronger.
  • If you drop something from a great height (tall building, aeroplane), gravity will make it accelerate as it falls down. However, the air pushes back on it, upwards (or more generally, in the opposite direction to the movement) and eventually will prevent the object falling any faster. (With air, the friction is directly related to the size and shape of the object and how fast it's going, but I won't get into the maths.) The maximum speed the object can reach while falling is called terminal velocity.
  • On the other hand, if there is no air — for example on the moon — there will of course be no friction from air and things like feathers which normally fall very slowly (because of all the little fuzzy bits catching on the air) will fall at the same speed and acceleration as a lead ball (or whatever). This will also work in a vacuum chamber where all the air has been removed. Here is a video of an astronaut on the last Apollo mission dropping a hammer and a feather at the same time:

    And a gif of the same if you can't be bothered watching and listening to the 47 second clip:

  • Brakes on cars and whatnot work by intentionally increasing the friction on the axle to slow down the spinning speed of the wheels
Now let's talk about how spaceships slow down in space. I want to emphasis that my complaint with Across the Universe wasn't that the spaceship was slowing down, but that it was slowing down by itself. Things can only slow down by themselves if there is friction around (so really they're not slowing down by themselves but because of friction, but we don't usually think about or notice friction so it seems like its happening by itself).

In real life, spaceships slow down (and manoeuvre) by firing their engines in the other direction. It might be a bit easier to picture on a smaller scale. Consider an astronaut on a spacewalk. Let's pretend they're not tethered to their ship and that the ship is out in deep space away from the gravitational influence of any planets. To be able to move around, the astronaut will have a gas tank (or similar) that will allow them to press a button to move forward. The gas will shoot out backwards for a couple of seconds, and the astronaut will move forwards. At this point, if the astronaut does nothing, they will continue moving in a straight line indefinitely. Basically until they run into something. The same thing happens with a spaceship: gravity and obstacles not withstanding, after it fires its engines for a bit to accelerate, it will keep going in a straight line at the same speed until something else happens to stop it. This clip from WALL-E is a good example (thanks to Shaheen for the suggestion). Also note that once they start spinning, things will continue spinning until something else makes them change, which you can see a bit of in that clip.

That doesn't mean things can't stop or slow down in space. Our astronaut — assuming they're not unconscious — can fire their gas in the opposite direction (to manoeuvre properly they'd have to have several directional options, six for complete manoeuvrability) to slow down. The spaceship can also fire thrusters in the opposite direction to slow down (either by having two sets or by rotating the main ones). Coming to an absolute complete stop is a bit tricky because a) you would have to balance forces very exactly and b) there's not much to use as a reference for how fast you're going out in space, but matching speeds with another ship is doable. And the astronaut slowing down enough to not break a wrist colliding with his ship is also useful. My older post about turning around in space addresses some issues with why just stopping and going in the opposite direction isn't the most efficient way of doing it.

The very last part of the question was:
So what does happen when you, in sci-fi, go from "warp speed" or whatever they like to call it, to, well, not?

The short answer to this is, whatever you want. Warp speed and hyperspace and other "let's cheat to go faster than the speed of light devices" aren't real. They're generally not based on real physics, or if they are, it's very extrapolated and speculative and could well turn out to be just as implausible. That said, faster than light travel is a staple of science fiction and I'm not suggesting we should eliminate it because it's implausible. If all science fiction stories used only slow or relativistic (which means close to the speed of light, when weird things happen. My post about it) then there'd be a lot of very slow stories which would get boring. Variety is nice.

As long as the rest of the science is plausible, then I don't have a problem with a bit of faster than light travel and faster than light communication. If the writer doesn't feel up to making up a semi-plausible sciencey explanation, then my personal preference is not to try explaining how the FTL works at all. Because they usually stuff up some minor point which annoys me disproportionately.

Monday, March 25, 2013

More thoughts on the importance of science in science fiction

Today I was directed to a blog post about how important science is in science fiction using the hideous crime against science example of Beth Revis's Across the Universe, which I blogged about here. (From the sound of it, the blog author may have read my post or someone else's similar reaction to the book.) The blog author asks how important is accurate science really, and is there a line? The rest of this post is based on my comment over there.

I think there is definitely a line. Stuff like faster than light travel, teleportation, artificial gravity (in some circumstances) are fair game to use in fiction with no or only hand-wavey explanations. (In fact, sometimes trying to be too specific with them can be detrimental.) Everyone either knows that stuff isn't real or can very easily google it to find out. And it has a distinct plot-based purpose: if everyone wrote relativistically accurate science fiction (no faster than light travel), it would be very boring. When getting from A to B isn't the point of the story, using an accepted trope to speed things up is totally fine. Same with power sources for spaceships. That's an area where there will definitely be heaps of progress in the future that we can't necessarily predict and so hand-waving is fine.

What isn't fine is getting basic and fundamental concepts wrong like the ship slowing down in space that Revis did. Note that she also had a hand-wavey power source in said spaceship and THAT is fine. But thinking there's friction in space? No. It's a popular book for teens and it's actively confounding a concept that's actually quite difficult to teach. Pretty much no one (and certainly no teen) has been in space and so books and movies are all most of us have to base our intuition on when it comes to how stuff in space works. For things on Earth, it's easy to think about our everyday experiences and predict (from a basic physics point of view) what will happen. On Earth, stuff DOES gradually slow down. In space it doesn't and that's a concept that some kids, when learning physics for the first time, find difficult to grasp. It's a disservice to further confuse the issue.

And for the record, usually if an author tries to do their research, it's obvious in the writing.


Now, when I was searching for a link to something Revis said in an interview about her research for this book (or lack there of), I came across the FAQ on her website. One of the questions and responses is:
Q: WAIT A MINUTE. I think I found a scientific error in Across the Universe.
A: Well–there’s a chance I messed up. BUT if you’re one of the ones who noticed the REALLY BIG scientific error…well, I’ll just say that there IS a sequel, and it DOES address this, and maybe it’s not that the book is wrong, but that the characters have the wrong idea…
I can only assume the "REALLY BIG" scientific error is the friction in space thing that's made me so angry. I'm not 100% convinced that it and associated sciencefails are properly addressed. I can think of one scenario that would make it "the characters are wrong but the science isn't", and from the plot of book one and the hints I've seen around the web for the events in books two and three, it doesn't seem likely.

Have any of my readers actually read the second book? Is it worth my time (and money) reading it just so I can blog about the problems in it? So far the answer to the second question has been "no" and picking up the second book in a shop and flicking through it didn't exactly fill be with the desire to jump back into that world.


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