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Lectures for a New Year: Neil deGrasse Tyson on Pluto

Neil deGrasse Tyson is ridiculously distinguished: the man holds at least fourteen honorary doctorates, not to mention his real doctorate in astrophysics. He was also declared "Sexiest Astrophysicist Alive" by Time Magazine in 2000. But he's most (in)famous for leading the charge to demote Pluto from its planet status to a "dwarf planet." (We made a shirt about that.) As Wikipedia explains:

As director of the Hayden Planetarium, Tyson bucked traditional thinking to keep Pluto from being referred to as the ninth planet in exhibits at the center. Tyson has explained that he wanted to look at commonalities between objects, grouping the terrestrial planets together, the gas giants together, and Pluto with like objects and to get away from simply counting the planets. He has stated on The Colbert Report, The Daily Show, and BBC Horizon that this decision has resulted in large amounts of hate mail, much of it from children. In 2006, the I.A.U. confirmed this assessment by changing Pluto to the "dwarf planet" classification. Daniel Simone wrote of the interview with Tyson describing his frustration. "For a while, we were not very popular here at the Hayden Planetarium."

In this talk, NDT talks to Google employees about his book The Pluto Files. I went through a lot of NDT lectures to find this one -- it stuck out partly because it's actually about Pluto, and partly because the tone is so wonderfully fun, smart, and I daresay geeky. All of his lectures are smart -- but this one is full of stories that make sense of planets, their history, and the work of scientists.

Topics: the history of planets, their discovery, and some of Tyson's own history, presented in conversational fashion with jokes. Also, the Q&A touches on The Matrix.

For: everyone, but especially people who are interested in space or history.

Representative quote:

"[In Roman times,] there were seven objects that would move against the background sky [including the sun]. ... Unambiguous! Everybody could agree that those were the planets." [Then everything got weird when Planet George showed up.]

Further Reading (and Viewing)

NDT is everywhere. He's about to host a reboot of the classic science program Cosmos, his Nova scienceNOW episodes are on Netflix, Hulu Plus, and free from PBS (albeit in slightly lower video quality). He even hosts a radio show. He has various books out (including Death by Black Hole), and the latest Space Chronicles: Facing the Ultimate Frontier lands in February, and of course the book he discusses above is The Pluto Files: The Rise and Fall of America's Favorite Planet (you might enjoy the brief 4-star Amazon review on that page...by Clyde Tombaugh's son!).

You'll almost certainly enjoy this Q&A with Tyson (he's feisty) and Stephen Colbert and Neil deGrasse Tyson in discussion.

Transcript

I haven't found a transcript of this lecture, but the YouTube/Google auto-captioning system works fairly well. It frequently mixes up proper nouns, but it's better than nothing.

Suggest a Lecture

Got a favorite lecture? Is it online in some video format? Leave a comment and we’ll check it out!

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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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