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How Do We Create, Define, and Search for Life?

Christoph Adami makes "artificial life," effectively self-replicating computer programs. If you've heard of Tierra*, that's the kind of thing Adami does. In this TED Talk, Adami discusses his work, including a brief discussion of how we define life on Earth -- which is lots of fun, as he describes a real-world organism that does not die. And no, we haven't been overrun by this monster (yet).

After the initial discussion of "what is life" (in the context of wanting to identify extraterrestrial life), Adami explains his own artificial life programs, and that's when things get deeply geeky. If you're interested in science of any kind, this talk is worth your twenty minutes. Stick around for the animations showing biodiversity, and then the animation showing how the rate of mutation affects populations -- it's strikes a very weird geek chord to see a fellow geek demonstrate his "it's alive!" moment onstage.

* = Brief personal anecdote on artificial life: in high school, I became interested in Tierra and similar systems. So for my high school's science fair circa tenth grade, I wrote a life simulator that attempted to demonstrate a form of "natural selection" (well, non-natural, but at least selection) based on mutation and competition within an artificial landscape. My project was a C program that created various artificial life forms (predators and prey) that competed in a virtual landscape, reproduced, mutated using an ultra-simplified DNA-ish structure, ate each other, died of old age, and so on. The program's output was text-only, indicating the genomes and population counts of dominant organisms. The program was so resource-intensive that I had to borrow computers to run it on, in order to actually demonstrate the system's long-term viability -- my home PC was so slow that a single "generation" took several minutes to run, and I needed to run thousands or millions to demonstrate the long-term effects of small mutations. Anyway, I won the Computer Science division of the fair (by virtue of being its only entrant), but didn't place overall. Oh well -- I learned that it's really hard to explain "artificial life" to non-geeks, so it's encouraging to see Adami's presentation, particularly his clever animation showing the mutation threshold necessary to sustain artificial life.

You might also enjoy a photo of me with an elementary school science fair project. I was working with real, plant-based life at the time.

(Via Hypercritical episode 67.)

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science
Here's What Actually Happens When You're Electrocuted
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Benjamin Franklin was a genius, but not so smart when it came to safely handling electricity, according to legend. As SciShow explains in its latest video, varying degrees of electric current passing through the body can result in burns, seizures, cessation of breathing, and even a stopped heart. Our skin is pretty good at resisting electric current, but its protective properties are diminished when it gets wet—so if Franklin actually conducted his famous kite-and-key experiment in the pouring rain, he was essentially flirting with death.

That's right, death: Had Franklin actually been electrocuted, he wouldn't have had only sparks radiating from his body and fried hair. The difference between experiencing an electric shock and an electrocution depends on the amount of current involved, the voltage (the difference in the electrical potential that's driving the current), and your body's resistance to the current. Once the line is crossed, the fallout isn't pretty, which you can thankfully learn about secondhand by watching the video below.

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Big Questions
Does Einstein's Theory of Relativity Imply That Interstellar Space Travel is Impossible?
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Does Einstein's theory of relativity imply that interstellar space travel is impossible?

Paul Mainwood:

The opposite. It makes interstellar travel possible—or at least possible within human lifetimes.

The reason is acceleration. Humans are fairly puny creatures, and we can’t stand much acceleration. Impose much more than 1 g of acceleration onto a human for an extended period of time, and we will experience all kinds of health problems. (Impose much more than 10 g and these health problems will include immediate unconsciousness and a rapid death.)

To travel anywhere significant, we need to accelerate up to your travel speed, and then decelerate again at the other end. If we’re limited to, say, 1.5 g for extended periods, then in a non-relativistic, Newtonian world, this gives us a major problem: Everyone’s going to die before we get there. The only way of getting the time down is to apply stronger accelerations, so we need to send robots, or at least something much tougher than we delicate bags of mostly water.

But relativity helps a lot. As soon as we get anywhere near the speed of light, then the local time on the spaceship dilates, and we can get to places in much less (spaceship) time than it would take in a Newtonian universe. (Or, looking at it from the point of view of someone on the spaceship: they will see the distances contract as they accelerate up to near light-speed—the effect is the same, they will get there quicker.)

Here’s a quick table I knocked together on the assumption that we can’t accelerate any faster than 1.5 g. We accelerate up at that rate for half the journey, and then decelerate at the same rate in the second half to stop just beside wherever we are visiting.

You can see that to get to destinations much beyond 50 light years away, we are receiving massive advantages from relativity. And beyond 1000 light years, it’s only thanks to relativistic effects that we’re getting there within a human lifetime.

Indeed, if we continue the table, we’ll find that we can get across the entire visible universe (47 billion light-years or so) within a human lifetime (28 years or so) by exploiting relativistic effects.

So, by using relativity, it seems we can get anywhere we like!

Well ... not quite.

Two problems.

First, the effect is only available to the travelers. The Earth times will be much much longer. (Rough rule to obtain the Earth-time for a return journey [is to] double the number of light years in the table and add 0.25 to get the time in years). So if they return, they will find many thousand years have elapsed on earth: their families will live and die without them. So, even we did send explorers, we on Earth would never find out what they had discovered. Though perhaps for some explorers, even this would be a positive: “Take a trip to Betelgeuse! For only an 18 year round-trip, you get an interstellar adventure and a bonus: time-travel to 1300 years in the Earth’s future!”

Second, a more immediate and practical problem: The amount of energy it takes to accelerate something up to the relativistic speeds we are using here is—quite literally—astronomical. Taking the journey to the Crab Nebula as an example, we’d need to provide about 7 x 1020 J of kinetic energy per kilogram of spaceship to get up to the top speed we’re using.

That is a lot. But it’s available: the Sun puts out 3X1026 W, so in theory, you’d only need a few seconds of Solar output (plus a Dyson Sphere) to collect enough energy to get a reasonably sized ship up to that speed. This also assumes you can transfer this energy to the ship without increasing its mass: e.g., via a laser anchored to a large planet or star; if our ship needs to carry its chemical or matter/anti-matter fuel and accelerate that too, then you run into the “tyranny of the rocket equation” and we’re lost. Many orders of magnitude more fuel will be needed.

But I’m just going to airily treat all that as an engineering issue (albeit one far beyond anything we can attack with currently imaginable technology). Assuming we can get our spaceships up to those speeds, we can see how relativity helps interstellar travel. Counter-intuitive, but true.

This post originally appeared on Quora. Click here to view.

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