## Thursday, August 13, 2009

### Impact (miniseries)

I just watched the second part of Impact, a German-American catastrophic TV miniseries (in the Czech dubbing) about our Moon that became 12 heavier by swallowing a "brown dwarf" and was otherwise determined to collide with the Earth before a team of unusually attractive astronauts and astrophysicists removed the 12-lunar-mass seed from the lunar core.

Like many other catastrophic movies, it was very emotional. And be sure that I am very sensitive about such matters that paint the sentiments of the people who see their beloved ones dying, deciding about the lives of others, or going to dangerous expeditions: yes, my reaction often includes tears. However, the underlying physics was just way too bad.

Their basic scientific story was that a bizarre heavy astrophysical object was absorbed by the Moon, our favorite natural satellite. People had some fun with cool meteor showers before they began to witness irregular anomalies - such as new kinds of thunderstorms, collapsing telecommunication networks, as well as trains and people floating above the ground. The elliptic orbit of the Moon was heavily distorted and only a few weeks of life were predicted before the eccentricity would have increased sufficiently dramatically for the Moon to hit the Earth. The mankind was getting ready for a judgement day.

A small bomb launched after a surgery of the Moon performed by a few astronauts (loving children, women etc.) managed to remove the brown dwarf seed - with 12 lunar masses of weight - from the conventional rest of the Moon. All people on the Earth could finally celebrate and expect a period of global cooling - probably caused by the dust created by the spectacular man-made explosion of the Moon that saved our civilization. ;-)

The trouble with their physics

Now, it's not clear to me whether the writers deliberately wanted the show to be scientifically ludicrous but the result can surely be classified by these words, and the fact that the average rating of the YouTube ABC trailer above is 2 stars, less than my rating, indicates that even somewhat ordinary viewers could find the scientific absurdities to be over the top and that the weak physics background has hurt the miniseries.

Of course, if you're very demanding about the accuracy, you know that there are no brown dwarfs that could be incorporated into the Moon. The celestial bodies referred to as "brown dwarfs" approximately weigh between 1 and 70 Jupiter masses - which is four orders of magnitude heavier than the object described in the Impact. There are no other heavy compact astrophysical objects that could do such a job. But you may always imagine that some new objects like that could exist. However, what they were doing with these new tools contradicted pretty much every single principle of physics, anyway.

An elliptical orbit simply can't change the eccentricity that quickly because everything besides gravity is negligible and gravity keeps the eccentricity qualitatively constant for millions of years: the Kepler problem produces exact ellipses, after all. Even if there were an enhanced electromagnetic influence from the Moon, it couldn't possibly be manifested by such strong effects on Earth, and certainly not by such spatially and temporally non-uniform events.

Even if you imagined that such irregular effects could occur, they wouldn't allow the electrically neutral people to float above the ground. Even if some unusual electromagnetic fields made them float, their motion would heavily depend on their composition because electromagnetic forces don't obey the equivalence principle (there were many other situations where the creators of the show were apparently confusing gravity and electromagnetism). Even if you imagine that neutral and iron-free humans could be attracted by forces that compete with the terrestrial gravity, it is extremely unlikely for these new acceleration terms to be exactly equal to "g" and to compensate the normal gravity (we would talk about "fine-tuning").

Even if all these things existed, the momentum conservation law would prevent the "brown dwarf", which is really the bulk of the new lunar mass, to dramatically change its trajectory after a collision with an irrelevant rocket: the filmmakers wanted the "brown dwarf" to dramatically change the gravitational behavior of the "new Moon", but they still wanted to think about the "old Moon" when it came to its mass, even though the "brown dwarf" was really the majority of the new object's mass.

I could go on and on and on. So if the miniseries is good at something, the something is surely not hiding in the credentials of the movie as a documentary that promotes the knowledge of physics, at least not the kind of physics that is called physics by your humble correspondent, and at least not without further discussions and corrections. ;-)

By the way, they never say that the "brown dwarf" had 12 lunar masses but it is a consequence of the fact that it has made the lunar surface gravity 2 times stronger than the terrestrial one, as they explicitly said, even though it is normally 6 times weaker (assuming that the brown dwarf was sitting in the center: the gravity of point masses and balls of the same mass is identical by Gauss's law). Normal brown dwarfs have masses between 20,000 and 1,500,000 lunar masses. While in the movie, they "sensibly" say that the gravitational acceleration at the surface of the "new Moon" was "2g", making the astronauts' job just a little bit harder, in the trailer above they also say that the new Moon was twice heavier than the Earth. These two statements are incompatible with each other (by a factor of six), because of the different radii (or equivalently different surface accelerations) of the Moon and the Earth.

They have clearly used no physics adviser who would be able to help even with such rudimentary calculations.

While 12 lunar masses is much less than the thousands or millions of lunar masses needed for a brown dwarf, it's still way too much for all their desired applications. With 12 lunar masses, they could figure out that it's impossible to "shoot" the object away from the orbit around the Earth, but it is also impossible for the eccentricity of its orbit to spontaneously yet quickly change that was needed to urgently threaten the Earth.

The problems, their solutions, and all their detailed features were completely wrong. But I must say that the filmmakers have still mastered at least the basic art of describing human relationships in extremely difficult situations.

Three stars. I appreciate many things, including the fact that the "brown dwarf" at least wasn't caused by the global warming like many similarly absurd effects in many catastrophic movies I recently watched. ;-)