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Man, I didn’t realize how long these were. I pasted the last one into word to check something and it was and a half pages long.
The back of the envelope calculation–scribbling down approximations in an equation and working it out to see if your guessed answer puts you in the right general range of where you should be. He cites an example from Battlestar Gallactica where he did some rough math to check to see whether someone would survive a hole being blasted into her ship. We’re working out the math, I guess, but the point is more that this kind of rough calculation can serve the purposes of fiction where we don’t really need specific numbers to see if something we want to do is possible.
Special relativity: there is no preferred reference frame (absolute uniform motion cannot be detected), which means in turn that there is no center of the universe, or possibly that every point is the center of the universe. There is a joke that used to say: a grad student meets Prof Einstein on a train and says, “Excuse me professor Einstein, does New York stop at this train?”
The speed of light is a constant, and it’s independent of the motion of the source. Imagine you’re at a train crossing and a flat car is going by at 60mph. There are people standing on the flat car. They are playing catch with a football, throwing it back and forth at a constant 10mph. Relative to you, the speed of the ball changes based on whether it’s going with or against the car (60+10, or 60-10). Now say that instead of throwing a football back and forth they are playing lasertag. The velocity remains C (the speed of light) whether it’s moving with or against the car.
The fact that C doesn’t change means that things we think of as fixed are not. Now mass will seem to change its value based on relativistic velocity. Now it doesn’t really change its mass, but it acts like it changes it mass. As it gets closer to the speed of light, it will act as though ti has more and more mass, until you hit the speed of light it acts as if it would hit infinite mass, thus requiring infinite energy to fuel it. You can’t hit the speed of light because you would act as if you had an infinite amount of mass.
Other weird things happen: e.g. Lorentz Contraction. If you are stationery and a space craft flies back and forth, at fractions of the speed and light, each time increasing, then each time you see it, it would appear to be compressed, more and more as the speed increases. In your frame, it is compressed. In its frame, you’re compressed. As you approach the speed of light, your length gets shorter, until you hit the speed of light at which point, you would act as if you had no length.
The speed of light is constant. Mass, time, length all change.
Special relativity also causes time dilation. As someone is moving relative to another, their clock will appear to run more slowly. A change in time of someone fixed is equal to the change in time over a person who is moving. This is called time dilation. The problem is that for the person in the spacecraft–in their frame–your clock appears to be running more slowly. That’s where it gets confusing. When you’ve seen in TV series that there has been someone who has aged a lot more than the other person there’s usually an implied round trip, and if there’s an implied round trip, there’s also an implied acceleration, which means that we have an objective point of view to tell whose clock really is moving more slowly.
But time is not fixed.Time moves at different rates.
Mass/energy equivalence– E=mc(2). Mass and energy can be converted.
General relativity is another thing that’s stated very simply, even though the implications are profound. In general relativity, a uniform acceleration is exactly equivalent to being in a gravitational field. So if I am in a craft accelerating at 1G, for you that is exactly equivalent to standing in earth’s gravity. There are profound ramifications. Imagine you have a very high-speed elevator and you have a hole in it and into that super-high-speed elevator you fire a lone photon, one particle of light; as this accelerates upwards, the particle of light, as it moves from one side of the other, will appear to arc down, but really it’s just moving horizontally.
Gravity will bend light. If gravity is the same as the scenario in the elevator, then gravity will bend light.
Another example of how spacetime is bent, we have gravitational lensing. If you are trying to observe a distant object, we see light bending around objects with enormous mass, causing the light to recreate an image of the object several times.
When we go to relativity, we don’t view gravity as an attractive force as we do under Newton. We believe that gravity is a warping of space. The common analogy is some kind of fabric pinned at the corners, with a bowling ball in the center. If you rolled marbles toward it, they would move around.
As we learned this, we experimented with starlight, and what we found from studying things like eclipses, we found that starlight is indeed bent.
Time/space/light/etc. rehash, ending in an explanation that astronomers talk about spacetime, and four dimensional space.
Black holes are really, really deep indentations into the space/time continuum.
In Sf, we have several ways to travel to other star systems. Using relativistic time travel, going at .7 the speed of light, you would functionally be at the speed of light, so you could go 4.3 light years in 4.3 years, though different periods of time would happen on earth.
There are ways posited to allow you to go around the FTL barrier. These may allow you to go FTL over the global, rather than local, region.
Wormholes: a clever term used to describe certain solutions to general relativity. There could be a point A in spacetime that is linked to point B where if you fire a ray of light at A you could go to point B. Until fairly recently, we knew that wormholes were microscopic; you could pass through a photon, but not a person. Recently, people have pioneered solutions to create macroscopic solutions (as determined by computational equations), though the stresses within those would still be a problem. They might be a way to pass communications through faster than the speed of light.
Kelly: I understand these are theoretically possible… have they been done in labs? Kevin: Not yet.
Ian: Traveling .7c is the same as the speed of light? Kevin: Yes, because of the Lorentz contraction; you’re compressed by .7, so from your point of view, you’d be at the speed of light. Theoretically, if you travel back through light, you would travel back in time. Can we make a time machine? Yes. We all move forward through time. Relativistic journeys let you do that even faster. It’s the backward part that’s questionable.
FTL: Another realm: Can we leave our realm and enter another one? We now believe that our N-dimensional universe is one of many immersed in an N+1 space. Our universe exists with several others like sheets in a book, side by side, non-overlapping, can’t necessarily get from one to another. (Some theorize this started the big bang, but that’s new and theoretical.) This is called the brane. All our universes are in a multiverse immersed in something called the bulk. So if you could leave at point A and enter the bulk–but who knows what the properties of the bulk are?–you could justify getting to point B. This is like Dr Who’s void.
FTL: Compress space. If you can warp or compress space ahead of you and then move yourself ahead of that, then you’d snap forward. That’s how Gallactica traveled in BSG even though it was never articulated in the show.
There’s a new notion people are taking seriously called the Alcubierre drive. He has solutions to general relativity that allow a Star-Trek-like warp drive that allow you to condense space in front of you and move through it. Further experiments show that within the warp bubble you’d have something in the order of 10^32 Kelvins.
The Gallactica drive is a jump, you compress space a lot, and then jump forward. The Alcubierre is to warp it locally and then move through it as you go.
John Joseph Adams: How much energy would it take to do any of this? It’s theoretically possible, but is it really so? Kevin: …Probably not. In SF, you have a gimme or two, and this would be one of them.
If we don’t travel rapidly, we can’t get to other stars in our lifetimes.
In BSG, they could have gone, at most, about 9,000 light years over the four years of the show.
Black Holes: A black hole is a black hole because there exists a region around the black hole called the event horizon, a theoretical surface where within that region the mass is so dense and so compressed that the escape velocity reaches the speed of light. That’s the so-called point of no-return. That’s why there’s no drama when a Voyager ship falls into the event horizon… the point of no return is the point of no return because the ev is the speed of light, but so what? Voyager can go way faster than that.
When you’re close to a black hole, you’re more worried about the tidal stress than the event horizon. The tidal stress on the leading edge of the object is so much greater than the force on the trailing edge that you’d be pulled apart–spagghettified.
You can find the radius for a black hole’s event horizon by calculating R = 2GM/C^2… that’s not huge. You have to get really close to a black hole before you reach the event horizon. You’re going to be pulled apart way before that happens, even with a hull made of (fictional metal).
Artificial gravity: All TV shows have artificial gravity because it’s too hard and expensive to simulate not having it.
There are ways to pretend you have artificial gravity. Let’s say we could create an artificial gravity generator. Gravity, as we note, is a radial force. So if you had a spherical ship with spherical decks, you’d be fine, but if you had just the one gravity generator in the ship, you’d be all on the walls.
Well, it’s always easier to miniaturize than to innovate. So say we have small gravity generators. So small we can put them in the floor. Say they’re down the center line of all your hallways. What do you get? A gravity field radiating cylindrically. So if your flow is bowed, you’re good. So your hallways in your spacecraft might be shaped like flared cylinders. (Wish I had diagrams for this.)
What if you put the fields down as grids? That’s what you’d have to do. BUT… what do the people in the floor below do? The floor below, you’d be stuck on the ceiling. This still gets complicated.
Ian: So they need gravity blockers to put in the ceilings.
When you think about the complexities of artificial gravity, you could use shoes with clips in them to clamp and unclamp, that would know when to turn on and turn off magnetic fields… smart shoes could approximate artificial gravity much more readily than something embedded in the floor.
Weaponry: Directed energy weapon is usually the weapon of choice in scifi. Directed energy is energy directed at somebody, and the absorption of that energy heats it up and it goes boom, or a hole burns through it and their air is vented. That’s something that’s interesting in space warfare where the kill criterion might be much lower–just vent their air.
Let’s talk about how they’re depicted. Why can you see laser beams, for instance, at rock concerts? Because there’s particulate matter in the air. You would not otherwise see this beam. In space, you would not see the beam, unless there’s a medium to scatter it (which also scatters your energy). A great example of where directed energy weapons were depicted well were hand-weapons for colonial warriors in original BSG. You don’t see the beam. Just the trigger pull, and the explosion. The cylons in series one were also silvered… lasers bounce off mirror, so that could work as defense. That was probably a coincidence, but it works.
Shadow vessels in B5 are also good, rather than a bolt, you see a cutting, slicing motion. You’d probably do that rather than poke a hole, unless you wanted to vent someone’s air.
On the moon, there’s something called corner cube reflectors. Take a cube, mirror the inside, and saw it off so you have the corner of a cube. Turns out that if you shoot a laser beam into that it will strike and bounce out the exact same way it came in, no matter what angle you fire it from. So the astronauts and also the soviets left corner cube reflectors on the moon. We use that to bounce beams off the moon to see how fast it’s receding from us (which is about 1 inch a year).
So interestingly, shine a laser beam into a corner, and it gets really, really bright, and that’s because the light is reflected in and coming right back. This isn’t related to weaponry, but it’s really cool.
JJA: So if you had a laser shooting at a mirrored cylon, and it bounced off, would you have like havoc in the room? Kevin: Maybe. It could hit someone. It could scatter. It would probably disperse on a non-reflective surface, but weirder things have happened.
So, directed energy weapons are often depicted incorrectly, but because they’re more pleasing.
Projectiles, though, are good in space, not low tech. They’d have caseless shells with their own oxygen and would fire. Projectiles also release way more energy. To mimic the amount of energy with the lasers, you’d need a lot of energy, with a lot of advanced power supplies or things that are very large. Bullets are really quite effective.
photon torpedo is antimatter in a containment vessel. the containment vessel goes off, the anti-matter touches the hull, pair annihilation, boom. anti-matter does exist. containing it is the key point to making weaponry.
one ounce of antimatter making contact with one ounce of matter would give you about four times the energy of a megaton nuclear weapon.
Force fields are real physics terms that have been abused by sci fi for a long time. A magnetic field is one such. So is gravity. But there is not something that you can use, nor is there likely to be something in the near future, that you can project to keep someone away–unless they’re charged, notes Ian. True, says Kevin, theoretically a magnetic field would keep away a particle beam.
Cloaking, however, is closer than you think. There are three lines of experimentation going on that would create practical invisibility. One involves a camera that would take a picture of what’s behind you and project it in front of you. Another is meta-materials which are materials whose optical properties relate to the chemistry of the molecule, and which can make infrared pass through it. There’s a third, but Kevin doesn’t remember what it is right now.
Now a cloaking screen (of meta-materials, I guess) should also be a deflector shield because if energy goes through it, meaning that you can’t see it, then energy used as a weapon would also go through it. A photon torpedo couldn’t hurt it because the blast of gamma rays would pass through it, unless the photon torpedo physically hit the cloak.
Kelly: smart shoes wouldn’t solve all the other physiological problems that humans have in zero G.
Kevin: true. when you go into space, you lose about 5% of your bone mass, which seems to be constant no matter how much time you spend up there, a day or a year. Gravity is a function of spin-rate. Higher spin-rate, more gravity.