Many of you are probably familiar with the show Game of Thrones on HBO based on the A Song of Ice and Fire novels by George R. R. Martin. To me, one of the most interesting aspects of the world that Martin creates is the seasonal cycle. For those of you unfamiliar, basically seasons can last many years at a time before changing. I have not been able to find exact numbers referenced, but it is implied that a season typically lasts around ten years. However, in the mythology of the world, some winters last much longer than that, though that only happens every thousand years or so. I found these cycles interesting and wanted to know if such cycles might have a scientific basis. Read on to find out what kind of explanation I came up with. Continue Reading
I recently discovered an old hoax saying that Rolling Rock was going to turn the moon into a giant billboard by projecting their logo onto it with a laser. Even though this was a hoax, the idea of advertising in space is not new. It is a common enough idea that it even warrants its own wiki page. I wanted to consider, from a physics perspective, some of the logistics that would be necessary to project an advertisement onto the moon. Continue Reading
So, as I pointed out before, last week was the annual APS March Meeting. For those of you unfamiliar with the conference, it consists of thousands of presentations given by professors, post-doctoral students, graduate students, and even undergraduate students. Most presentations are scheduled to last ten minutes followed by two minutes of questions for the speaker. This schedule is enforced by the chair of the session. This person is tasked with deciding how many questions should be asked and informing the speaker if they are running out of time. I noticed as the week went on that the talks always seemed to be rushed toward the end and there were often very few questions allowed by the session chair. This observation brought out the scientist side of me. I decided to take data and determine how long the talks were actually taking. So, this is what I did: starting on Thursday, I timed each presentation I went to and recorded the time at the end of the presentation and then again at the end of the question period. To see the results of the experiment read on! Continue Reading
I was recently watching an episode of The Universe, the show from the History Channel, which detailed ten different ways to destroy the Earth (Season 4 Episode 6). One of the proposed destruction techniques was to instantly stop the rotation of the Earth. This would cause everything on the surface of the Earth to be violently thrown as the ground beneath it instantly stands still. It would be quite a violent stop. For some perspective, in New England, where I am located, you would be thrown at a velocity of about 800 miles an hour to the East. It is very unlikely that anybody could survive an impact with anything at that speed. That is not to mention that every building would be thrown at that velocity as well. However, the contributors to the show, professional astrophysicists, claimed that if you could survive the initial stop it is still unlikely that you could survive the aftermath. Specifically, the atmosphere would not be stopped, so there would be windspeeds of up to 1000 miles per hour as it continued rotating at its initial velocity. The show claims that this wind would create so much energy that it would heat up the atmosphere enough to melt rock. This claim seemed a bit too dramatic to be true, so I decided to do some calculations to see how credible it is. Brace yourselves, quite a bit of math is ahead as we fact-check…The Universe! Continue Reading
For those of you outside the physics community something big is happening next week that you may not know about. It is the annual March Meeting of the American Physical Society (APS). It is the single largest physics conference in existence and it just so happens to be taking place in Boston this year. To give you an idea how big, last year, there were over 7700 submitted abstracts meaning that there were that many people with posters or giving a talk about their research. That does not include the thousands more physicists that go to keep up with current research and foster collaborations with other groups. Needless to say, I will be there almost all of next week soaking it all in as it will be the first conference I have ever been to. I will try to post updates about the meeting throughout the week so stay tuned!
For more information on the March Meeting check out the official site here and the list of submitted abstracts here (pdf).
There has been quite a bit of press about construction of a space elevator by Obayashi Corp, a Japanese construction company, lately. As exciting as an elevator to space would be, let’s just look at some of the hurdles that such a project would have to overcome from a scientific point of view.
What may not be obvious to non-physicists is how you would keep an elevator to space from falling back down to Earth. It would, in some sense, be the tallest thing mankind would have ever constructed, but you can’t just build a really tall building into space. Instead, you would have to assemble a giant platform in geosynchronous orbit (altitude 36,000km) and then lower the elevator cable from space. This would allow you to build the elevator from the top down. However, the plans proposed by Obayashi propose extending the elevator to 96,000km. This means that if the top of the elevator were not connected to Earth in any way, it would orbit slower than the Earth rotates. When you connect the two, the Earth would actively pull on the top platform, speeding it up to match the rotational speed of the Earth. This makes sense from a construction point of view; having the platform want to fly away from the Earth means that you can pull on the cable in order to climb it without pulling the elevator down on top of you.
A schematic of how a space elevator would have to be built.
Even though the top of the elevator has to be pulling on the Earth to keep tension in the cable, it is a productive exercise to figure out just how much tension would be produced from something at that altitude. First, we need to make a few assumptions. Let’s assume the counterweight at the top of the elevator has about the same mass as the International Space Station (450,000kg) and for now let’s ignore the mass of the cable connecting the counterweight and the Earth.
It is easy enough to write down the force on the counterweight due to the gravity of the Earth. Newton figured it out centuries ago:
Fearth = -G M m/r2
where G is the gravitational constant, M is the mass of the Earth, m is the mass of the counterweight, and r is the distance to the center of the Earth.
Meanwhile, the force from the Earth accelerating the counterweight to match the rotation speed of the Earth is given by:
Frotation = m ω2 r
where ω is the rotation velocity of the Earth.
The sum of these two forces is what acts on the counterweight:
Ftotal = -G M m/r2 + m ω2 r
At an elevation of r=102,400km (the altitude plus the radius of the Earth), Ftotal = 227,799 Newtons. This is equivalent to the weight at Earths surface of a 25 ton object. In construction terms however, that is not too bad; many things weigh much more than that are suspended by cables. However, the cables used to make such an elevator would have to stretch almost 100,000 km; about 100 times longer than any current cable in existence! Not only that, but when you factor in the weight of the cable itself, it is not feasible unless the material it is made of has a much higher tensile strength/mass ratio than steel. Currently the only material that has such a high ratio is carbon nanotubes, but the longest continuous piece of carbon nanotubes was 2cm long made at MIT, not even close to useful lengths.
So, due to the limited manufacturing capability of carbon nanotubes, the space elevator is likely to remain a lofty dream for the foreseeable future. This doesn’t mean we can’t imagine what it would be like to visit the top of the space elevator. For instance, if you were way up at the counterweight, you would not be weightless like the astronauts in the ISS. Instead, you would actually feel a weak force pushing you away from the Earth, about 1/20th that of gravity on the surface of the Earth. This means that in order to not fly away and off into space, you would either have to stand with the top of your head facing the Earth or somehow tether yourself to the counterweight. This would have to be considered when building the elevator car. When you start your journey on the Earth, you would experience normal gravity. However, that gravity would slowly decrease until you reached and elevation of 36,000km where you would be weightless. Then, as you climbed more, you would experience a force pushing you into the ceiling. That means what started as the ceiling became the floor and when you travel back down to the planet, you would have to switch one more time. So, controls, storage, facilities, etc. in the elevator car would need to be able to operate regardless of the apparent direction of the force of gravity.
Which mode of transporation is more awesome: The Knight Bus or The Cat Bus?
For those of you unfamiliar with these two “vehicles,” the Knight bus is from the world of Harry Potter. It picks up wayward wizards on the British Isles and takes them wherever they want to go in magical style. The Cat Bus is from the world of Hayao Miyazaki’s My Neighbor Totoro. It picks up little girls that get lost and takes them home. To see the two in action, check out the videos:
I think this argument is pretty cut and dry. The Knight Bus is a superpowered triple-decker bus that can take you anywhere you want to go on the British Isles. It is the pinnacle of wizardly ground transportation. The Cat Bus on the other hand is a freak of nature. Just take a second and try to imagine the anatomy going on inside the cute and fuzzy exterior. What does the Cat Bus’s skeleton look like, especially considering the fact that it can just open up a door in its side at will. That brings me to another point, the Cat Bus is alive. It would need to eat and expel waste. If you think car exhaust smells bad, then just imagine a Cat Bus garage. My final point is that we can easily tell the Cat Bus is some accident spawned from a radioactive wasteland just by the fact that its eyes are its headlights! That’s right, glowing eyes. So, in conclusion, the Knight Bus represents a pinnacle of man’s achievement while the Cat Bus represents the worst side of nature’s folly and therefore the Knight Bus is more awesome than the Cat Bus.
To check out the counterpoint, go here.
