Solar sail

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Okay, I’ve got a question for anyone who’s studied more physics than I have. I’m going to expose my woeful ignorance of modern physics. (I’m a medical ethicist MA student who did philosophy/pharmacology and toxicology for his undergrad, after all.)

Periodically, I see an article or a sci-fi programme on space flight that discusses the possibility of using a solar sail to power the movement of a space ship. Cool idea.

As best I can put it together, the idea is as follows:

  • The sun shines its photons out in all directions.
  • The photons hit the sail, imparting their momentum to the sail, pushing the space ship.
  • The space ship flies away from the sun, pushed by the photons from the sun.

I Googled solar sails and found the Wikipedia article on radiation pressure, and apparently it’s a measurable thing that a certain amount of pressure is placed on a surface that is in contact with a certain amount of radiation.

It sounds pretty neat, but here’s the thing I never understood. Probably because I only ever took first-year physics in my undergrad. If I’ve messed something up here, let me know.

  • The momentum (p, a vector quantity) of an object is the product of its mass (m, a scalar) and its velocity (v, a vector that is, of course, a scalar multiple of p), or p = mv
  • For an elastic collision, the vector sum of the initial momenta is equal to the vector sum of the final momenta, or p1 + p2 = p1′ + p2′ (where p1 is the initial momentum of the first object, p1′ is the final momentum of the first object, etc.).
  • As I recall, the mass of a photon is 0 kg. That’s not just because of rounding—photons are entirely massless.
  • So the mass of object 1, the photon, is 0 kg. The velocity of object 1 is c [away from the sun]. (When you write “c” in physics, it means “the speed of light.”)
  • Let’s take the mass of the space ship to be m2 and the initial velocity to be 0 m/s [away from the sun], assuming it starts at rest, relative to the sun.
  • Plug this all into the formula for an elastic collision:
  • m1 v1 + m2 v2 = m1 v1′ + m2 v2′
  • (0 kg) (c) + m2 (0 m/s) = (0 kg) v1′ + m2 v2′
  • 0 kg m/s = m2 v2′
  • v2′ = 0 m/s [away from the sun]

So, the final velocity of the space ship is still 0 m/s [away from the sun].

I really don’t get it.

No matter how many massless photons you shoot at a solar sail, you will never impart any momentum to the space ship, because a photon can’t have any momentum, because photons are massless.

I have a hard time believing that no one has thought of this before. Is there anyone out there who is better at physics than I am who can explain to me why solar sails work?

BibTeX

@online{bgcarlisle2011-1621,
    title = {Solar sail},
    journaltitle = {The Grey Literature},
    author = {Benjamin Gregory Carlisle},
    address = {Montreal, Canada},
    date = 2011-04-12,
    url = {https://www.bgcarlisle.com/blog/2011/04/12/solar-sail/}
}

MLA

Carlisle, Benjamin Gregory. "Solar sail" Web blog post. The Grey Literature. 12 Apr 2011. Web. 22 Mar 2019. <https://www.bgcarlisle.com/blog/2011/04/12/solar-sail/>

APA

Carlisle, Benjamin Gregory. (2011, Apr 12). Solar sail [Web log post]. Retrieved from https://www.bgcarlisle.com/blog/2011/04/12/solar-sail/

An alternate ending to Avatar

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So Avatar seriously missed out on a major marketing opportunity. I went to see it with a classmate of mine in mid-January, although during the film, I started to feel bad (headache, dizziness, sore throat, etc.) and I probably should have just gone home. Instead I saw the film and I also went out for Mexican food with them afterward. I was in so much pain. Poor judgement on my part.

Anyway. If you haven’t seen Avatar, don’t read the following. I’ll spoil the film for you.

I think a minor plot change toward the end of the film would have helped out Avatar greatly. The writer should have made Sully (the hero) permanently switch bodies with his avatar before the big action finale, rather than after. This would have produced three major advantages.

1. This would have provided a shocking moment of dramatic tension at the end of the film.

In the last struggle between the villain (whose name I’ve forgotten—Colonel Quidditch, I think?) and Sully, the villain could have destroyed Sully’s (now dead) human body, while the audience still thinks that Sully is inside it. There is a moment when all hope seems lost, and then Sully’s avatar body could spring back to action and kill the villain when he lets his guard down. Later, the audience would realise that Sully switched bodies the night before the battle, the way that Ellen Ripley tried (and failed) to, earlier in the film.

Tolkien coined a term for these moments. He called them, “eucatastrophes.” We really like it when stories end with a eucatastrophe. It’s satisfying to see parts of a well-told story come together to bring the hero to a point of seemingly utter defeat and then to glorious victory. We experience a wide range of emotion and that can be very cathartic.

2. Second, this would eliminate one of the endings, and shorten the film. We already saw the botched body-switching with Ripley, earlier in the film. We didn’t need to see it again. The movie’s too long anyway. Or maybe I just felt that way because when I went to see it I was coming down with the symptoms of a nasty viral infection.

3. The third major advantage that this would provide, is that the movie could then be marketed toward Evangelical Christians. If they had changed the plot in the way I suggest, it would suddenly become a Christian allegory.

A chosen one comes into a world from the heavens and takes on the flesh of the men who live there. He dies and rises again, draws all the nations to himself, and saves the world.

All you would need is a short Biblical message from Kirk Cameron at the end and you could probably even get Fred Phelps’ approval for this movie. Unless, according to Fred Phelps, God hates blue, spiky-eared, cartoon aliens as much as he seems to hate everything else. (By the way, did you know that God hates Twitter?)

Oh wait. On second thought, I take it back. Fred Phelps would never approve of this movie, because everyone in it smokes cigarettes. And if there’s one thing that Fred Phelps has taught us, it’s that God hates fags. That’s what he meant, right?

I came out of the theatre, and all I could think about was all the embodied mind and cognition stuff we learned in Merleau-Ponty class. Those who have read my blog know how I feel about Merleau-Ponty. Sometimes I’m afraid I will have Merleau-Ponty nightmares again. The ones where everyone speaks in Phenomenology. In my Merleau-Ponty nightmare, they all use words like:

  • Tacit cogito
  • Prenoetic I can
  • The being (sometimes as distinguished from the becoming)
  • Phenomenal field
  • Our being-in-the-world

I haven’t got a clue what any of these things mean. If someone can enlighten me, please do.

And at the end of the nightmare, everyone turns to me for comment. I shuffle papers nervously, clear my throat and scream on the inside. But there is no escaping Merleau-Ponty.

BibTeX

@online{bgcarlisle2010-623,
    title = {An alternate ending to Avatar},
    journaltitle = {The Grey Literature},
    author = {Benjamin Gregory Carlisle},
    address = {Montreal, Canada},
    date = 2010-01-31,
    url = {https://www.bgcarlisle.com/blog/2010/01/31/avatar-alternate-ending/}
}

MLA

Carlisle, Benjamin Gregory. "An alternate ending to Avatar" Web blog post. The Grey Literature. 31 Jan 2010. Web. 22 Mar 2019. <https://www.bgcarlisle.com/blog/2010/01/31/avatar-alternate-ending/>

APA

Carlisle, Benjamin Gregory. (2010, Jan 31). An alternate ending to Avatar [Web log post]. Retrieved from https://www.bgcarlisle.com/blog/2010/01/31/avatar-alternate-ending/

Mom’s amaryllis

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Mom's amaryllis

Mom's amaryllis

Here is mom’s amaryllis plant. It was a gift from a friend, but I can’t remember who.

She says it reminds her of something from Dr. Seuss, with the bloom-within-a-bloom. I say it’s kind of like Alien, with a mouth-within-a-mouth.

BibTeX

@online{bgcarlisle2009-567,
    title = {Mom’s amaryllis},
    journaltitle = {The Grey Literature},
    author = {Benjamin Gregory Carlisle},
    address = {Montreal, Canada},
    date = 2009-12-28,
    url = {https://www.bgcarlisle.com/blog/2009/12/28/moms-amaryllis/}
}

MLA

Carlisle, Benjamin Gregory. "Mom’s amaryllis" Web blog post. The Grey Literature. 28 Dec 2009. Web. 22 Mar 2019. <https://www.bgcarlisle.com/blog/2009/12/28/moms-amaryllis/>

APA

Carlisle, Benjamin Gregory. (2009, Dec 28). Mom’s amaryllis [Web log post]. Retrieved from https://www.bgcarlisle.com/blog/2009/12/28/moms-amaryllis/

I just remembered

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District 9

District 9

I just remembered why it is that I posted my review of District 9 under bioethics.

[There is a medium-grade spoiler in this post, so if you want to know nothing about the film before you see it, stop reading.]

I realised while watching the movie that my bioethical training has been having an effect on me. There is a scene toward the beginning of the film, where the main character is about to be cut up and his organs harvested for scientific experiments, against his will, while he is still conscious. When I saw that, I was struck with the horror of the idea of that happening to someone, but in my mind, all my objections were couched in the language of academic bioethics:

“He has not given informed consent for this research!”

“They are breaking the Dead Donor Rule!”

“That action is contrary to all four of Beauchamp and Childress’s principles of medical ethics!”

If you can name all four of Beauchamp and Childress’s principles, then you get 8 points. Two for each one.

BibTeX

@online{bgcarlisle2009-468,
    title = {I just remembered},
    journaltitle = {The Grey Literature},
    author = {Benjamin Gregory Carlisle},
    address = {Montreal, Canada},
    date = 2009-11-25,
    url = {https://www.bgcarlisle.com/blog/2009/11/25/i-just-remembered/}
}

MLA

Carlisle, Benjamin Gregory. "I just remembered" Web blog post. The Grey Literature. 25 Nov 2009. Web. 22 Mar 2019. <https://www.bgcarlisle.com/blog/2009/11/25/i-just-remembered/>

APA

Carlisle, Benjamin Gregory. (2009, Nov 25). I just remembered [Web log post]. Retrieved from https://www.bgcarlisle.com/blog/2009/11/25/i-just-remembered/

It was much better than I thought it would be

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District 9 Poster

District 9 Poster

District 9 was a very good movie. I was surprised. I didn’t think that I would like it, but Pickles and I went to see it and it was certainly worth our time.

There is certainly violence in this movie, but the violence wasn’t gratuitous—it always serves the storyline.

The story itself is engaging and I found the characters convincing. The story also serves to make a commentary on human nature, generally.

This is very grown-up sci-fi, in that the aliens are not there just because it’s cool to put funny make-up on people. (To be honest, I think they were computer-generated anyway.) The way that they look is an essential part of the telling of the story. One immediately has a gut reaction against the “prawns,” due to their physical appearance. The way that one comes around to see things from the perspective of the aliens by the end of the film is a very clever bit of storytelling, and it’s worth the time to watch it.

I liked the way that it ended, with a bit of mystery. As much as I liked this film, I don’t think I would want to see it again, though. It was really quite graphic.

BibTeX

@online{bgcarlisle2009-463,
    title = {It was much better than I thought it would be},
    journaltitle = {The Grey Literature},
    author = {Benjamin Gregory Carlisle},
    address = {Montreal, Canada},
    date = 2009-11-20,
    url = {https://www.bgcarlisle.com/blog/2009/11/20/it-was-much-better-than-i-thought-it-would-be/}
}

MLA

Carlisle, Benjamin Gregory. "It was much better than I thought it would be" Web blog post. The Grey Literature. 20 Nov 2009. Web. 22 Mar 2019. <https://www.bgcarlisle.com/blog/2009/11/20/it-was-much-better-than-i-thought-it-would-be/>

APA

Carlisle, Benjamin Gregory. (2009, Nov 20). It was much better than I thought it would be [Web log post]. Retrieved from https://www.bgcarlisle.com/blog/2009/11/20/it-was-much-better-than-i-thought-it-would-be/

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