Q: What would happen if a black hole passed through our solar system?

Posted on February 21, 2012 by Astronomer

Astronomer: Most black holes form when a star which is ten times more massive than our Sun runs out of fuel for fusion. This causes the star to collapse, explode as a supernova, and, if enough material is left over after the explosion, becomes what is called a stellar black hole. A black hole is an object with such a high density that even light doesn’t travel fast enough to escape its gravity. Something that falls into a black hole can never escape, because nothing can travel faster than the speed of light.

What would happen if one of these stellar black holes wandered into our solar system? Very Bad Things. The first indication we might get that something unusual was happening would be subtle changes in the orbits of the outer planets. These changes would be detectable at least by the time the black hole was a few hundred thousand times the distance between the Earth and the Sun.

By then the black hole would be near the outer reaches of the solar system, in an area filled with icy comet-like objects called the Oort cloud. It’s possible that the gravitational disruption caused by the black hole traveling through the Oort cloud could gravitationally catapult a large number of additional comets into the inner solar system, some of which might strike Earth or other planets. If the black hole passed through only this outer part of the solar system, for example if it were moving too fast to be strongly affected by the Sun’s gravitational influence, an increase in comets in the inner solar system might be the only effect we would observe.

At this point we likely wouldn’t see anything at the black hole’s position, even if we looked with the best available telescopes. The black hole itself doesn’t doesn’t give off light, and the only way we might detect it is through the energy released when it consumes some gas. Even the black hole’s affect on the light from stars behind it – which causes the light to be bent into an apparent ring around the black hole – would be too small for us to see. Only until the black hole reaches the inner edge of the asteroid belt would we be able to directly observe the light-bending effects of the black hole. By this point, the effects on the Earth’s orbit would be extreme and it’s likely the black hole would have become visible through its interaction with one of the outer planets.

If the black hole continued to move toward the inner solar system, the orbits of the planets would continue to be disrupted in dramatic ways. Jupiter, the most massive planet, might be snared by the black hole due to their strong mutual gravitational attraction. The black hole would pull gas from Jupiter, forming a bright disk of swirling, hot gas. The hot gas disk gives off x-ray radiation. Despite the fact that Jupiter is thousands of times larger than the black hole, the black hole is thousands of times more massive than Jupiter and easily wins. Jupiter is entirely consumed onto the relatively tiny black hole.

A black hole eating the sun. Om nom nom.

By this time, the Earth is already in grave trouble. The gravitational effects of the black hole have caused earthquakes and volcanic eruptions more extreme than those ever seen before by humans. The Earth would be pulled out of its usual orbit, possibly experiencing abrupt changes in direction or being pulled away or towards the Sun. By the time the black hole crosses Earth’s orbit the geologic effects from tidal forces will have effectively repaved the Earth’s surface with magma and wiped out all life. Since the Sun contains 99.9% of the mass of the solar system, the Sun and the black hole experience a strong gravitational pull towards each other. The black hole would approach the Sun, whose gas is stripped and pulled into the black hole. The Earth, whose inhabitants have already died, would approach the sun/black hole pair, heat up, be torn apart by gravitational forces, and then be pulled into the black hole itself.

Now that we’ve set this morbid scene, you might wonder how likely is it that a black hole will wander into our solar system, causing widespread death and destruction. Here, at least, we have some good news. With what we know today, it seems exceedingly unlikely to happen anywhere in the galaxy (except at the very center), much less our own solar system. Distances between black holes are huge, and the density of black holes is less because we are in the outer third of our galaxy. In addition, most black holes aren’t zipping around the galaxy at high speed, which makes them far less likely to encounter a solar system.

(picture credit: University of Warwick/ Mark A. Garlick)

Posted in -- Guest Author, Astronomy, Paranoia, Physics | 81 Comments

Q: If you are talking to a distant alien, how would you tell them which way is left and which way is right?

Posted on February 16, 2012 by The Physicist

Physicist: Assuming this question isn’t about interstellar political leanings, the answer is: it’s tricky, but it can be done.

This is worth trying out just once in your life.  Try to define left and right for someone using only physical principles, and without making reference to anything else.  So you can define “down” by asking the other person to hold something out and then drop it, but you can’t define down as “the direction the Eiffel tower isn’t pointing” (for our Parisian readers).  You’ll find that any (successful) attempt you make to distinguish left from right involves citing example.

For example, "Left" can be defined as the relative position of Washington as compared to Lincoln when viewing Mt. Rushmore from the front.

If an alien is so distant that there are no common landmarks (spacemarks?) that you can both see, then you’re restricted to just using experiments.  You can cheat by sending your signal using circularly polarized light, but let’s not cheat.

For a long time it was assumed that the universe can’t tell the difference between right and left, since every physical law seemed to work exactly the same right-ways as left-ways (Also, since the universe has no thumbs it can’t make an “L” with its left hand).

However, the dawning of the nuclear age heralded a new age of handedness.  It turns out that if both you and your alien friend have access to decent laboratories, then you can describe left and right using only physical principles.

Some nuclear processes (specifically “β– decay” in what follows) can tell between left and right.  Or more accurately, they can tell the difference between right and left-handed “chirality” (this post talks about chirality in passing).  So if you get something like radioactive cobalt and stick it into an extremely strong magnetic field you’ll find that the radiation it produces tends to stream out in one direction, which allows you to tell the difference between right-handedness and left-handedness.

One way is to notice that to produce the magnetic field you need to run electrical current in a loop, and the direction of the radiation stream allows you to define whether the current is running clockwise or counter-clockwise (in one case the radiation is toward the ring and in the other it points away).  Once you’ve defined clockwise and counter-clockwise, left and right is easy.

There is a caveat.  If the same experiment is done on anti-matter, then the results are reversed.  So, say you both run the experiment and find that the radiation comes out of the top of both of your devices.  While you both think that you’ve managed to communicate left/rightness, you’ll find that you’re mistaken.

But it won’t be until you invite your alien friend to Left-hander’s day that you’ll discover the mistake.  Hopefully you’ll manage to catch it before they land their anti-matter spaceship, which would be a bad day all around.  Bringing anti-matter and matter together results in the complete annihilation of equal amounts of both, and the release of all of their energy (which is a lot).

If after doing the experiment to establish right and left the alien shows up looking like this, then don't shake their hand. That dude's made of anti-matter.

Luckily, there doesn’t seem to be any anti-matter floating around the universe.  At least, not much.  So, if you know that you and the alien are both made of matter (which is pretty certain to be the case), then you can tell the difference between left and right.

Posted in -- By the Physicist, Particle Physics, Physics | 26 Comments

Q: Would it be possible in the distant future to directly convert matter into energy?

Posted on February 10, 2012 by The Physicist

Physicist: You hear about nuclear devices taking advantage of “E=mc2” to turn matter into energy, so nuclear power seems like it might be a good way to go.  But it so happens that everything that releases energy loses mass in the process.  The statement that nuclear devices turn mass into energy, while true, is giving them more credit than they deserve.  Even a wind-up clock loses mass as it winds down (just not much).  Any kind of energy that you can tie up in matter; chemical, nuclear, electrical, whatever, genuinely increases the weight of the object in question.  A charged 9-volt battery, for example, literally weighs about a tenth of a nano-gram more than an absolutely identical uncharged battery.  But it’s hard to notice an increase of one part in 500 billion.

What this question is about is a process like: step 1) take a brick, step 2) turn it into energy and no brick.

The process in question: start with matter, end with energy.

In order to convert matter into energy requires us to get past a few conservation laws.  These are the conservation laws that keep us from turning into energy just whenever.  For example, there’s a conservation law that says that the total number of protons + neutrons has to stay the same forever, and there doesn’t seem to be an easy way around that.

But there may be a cheat!  A difficult way, if it’s possible at all, to circumvent the conservation laws may be to create a tiny black hole, feed it matter, and collect its “Hawking radiation“.  Black holes aren’t very particular about what kind of energy or matter they absorb, and the Hawking radiation they produce is mostly just light.  So, problem solved!  Make a black hole, feed it any kind of matter, and collect the energy it generates.  But, there’s a whole lot involved in that that’s impossible, or nearly impossible.  Despite all of the hoopla surrounding CERN, creating artificial black holes is pretty difficult.  Even if they had managed to create a black hole, the kind that we’d need would have to be just a whole lot bigger.

Hawking’s whole thing is that a black hole, through some pretty fancy quantumy tricks, radiates energy as though it were hot and that the temperature that it acts like it has is greater the smaller the black hole is.  The black holes that exist today are huge and extremely cold (much colder than even the back ground radiation of the universe).  But, as a black hole radiates energy it loses mass and shrinks, which makes it “warmer”, which makes it radiate hotter, and so on.  So, oddly enough, if you want to get a black hole to radiate more energy you need it to be smaller.

Powering humanity takes about 17 trillion watts, which would require a black hole no more massive than 4.6 million metric tons and no larger than 0.0000000000000000014 meters (14 attometers) across.  Black holes are hella dense.  The bad news there is that a black hole that small can’t “eat”, because it’s already smaller than any particle (electrons, the smallest particle, are 400 times larger), so nothing will fit into its “mouth”.  Technically, for quantum-ish reasons, it’s more accurate to say that it’s unlikely that the black hole would be able to eat an available particle.

A “feedable” black hole, assuming you could get the particle guns perfectly lined up to fire matter into it (even as it’s basically exploding) would need to be at least, say, proton-sized.  That puts a cap on it’s power output at a measly 200 mega-watts, give or take.  You can’t even power a flux capacitor with that.

Quick aside: This stuff here about “feedability” and whether or not particles can fit into a black hole are non-issues.  Black holes “burn” long enough that they do not continuously need new matter.  This was a mistake born out of misunderguestimation.  There’s a correction at the bottom of this page under “my bad!”.

So, maybe, in the far off future we could (somehow) create thousands of tiny black holes and harness them for power.  Harvesting energy from micro-black holes is a tricky business and they’d have to be kept off-world, somewhere in space.  Unlike other power sources, they can’t be turned off, and on a strictly practical note, when something weighs a few millions of tons and is smaller than the point of the world’s sharpest pin, it’s difficult to hold on to.  It would fall through the floor of your power station faster than you could say “hey, who left this black hole over here?” so orbit or higher is really the way to go.

Long story short, there are easier, safer ways to get power than matter annihilation and black holes.  Although it’s still a much better option than coal.

By the by, while the physics behind them is horrifying the equations governing Hawking radiation are pretty clean.  The power output, P, for a black hole of mass M (in watts and kilograms) is P=\frac{3.56\times 10^{32}}{M^2}.  Or, using the black hole’s radius (in meters), P = \frac{7.82\times 10^{-22}}{R^2}.

My bad!: A concerned reader pointed out that you don’t need to keep feeding a micro black hole to get power out of it.  They stay hot for so long that you can set it and forget it.  All the same, you still need to get a tremendous amount of material into an impossibly small region to get the ball rolling.

In the case of a 4.6 million ton black hole capable of powering Earth, you can expect it to keep going strong for over 250 thousand years.  In fact, it’s power output would increase substantially with time.  The danger is that civilization may forget to move their black hole power sources far away before they burn out.  In the last minute of a black hole’s life it destroys about 1 megaton of matter, which translates to about 1.5 billion “Little Boy” bombs, with about a fourth of that being radiated in the last second.  Not the sort of thing that should be parked in orbit.

Power output of a black hole in gigawatts vs. time in years, starting at an output of 17 trillion Watts.

The black hole’s last few decades aren’t particularly pleasant either.

By the way, if you feel the need to run through this sort of thing yourself, the mass of a black hole at a given time, t, is M(t) = \left( M_0^3 - 1.19\times 10^{16}t\right)^{1/3}, where Mo is the initial mass.  It’s easy enough to figure out how much energy that translates too: E=Mc^2.

Posted in -- By the Physicist, Mistake, Particle Physics, Physics | 27 Comments

Q: What’s the difference between anti-matter and negative-matter?

Posted on February 4, 2012 by The Physicist

Physicist: Anti-matter is exactly the same as matter, but different.  If you, and everything else on the planet, were suddenly turned into anti-matter, you’d never know the difference.  While the “anti-” of anti-matter may seem to give it an air of mystery, it still acts just like ordinary matter in essentially every respect.  Specifically, anti-matter carries positive energy and mass, just like regular matter, while negative matter carries negative energy and mass.

Famously, when you bring matter and anti-matter together they annihilate.  All of their combined mass is converted into buckets of energy in an amount dictated by Einstein’s little-known equation, E=mc2.  For comparison, the largest nuclear device ever detonated, the USSR’s “Tsar Bomba”, is the yield you’d expect from about 1 kg of anti-matter (so about 2 kg of energy total, because it needs some mass to annihilate with).  A single atom of anti-matter (say, anti-carbon) annihilating in your ear would be just barely audible as a pop.  It’s the energetic equivalent of a ant stomping a foot (in anger!).

Negative matter, more commonly called “exotic matter”, has negative energy.  If you were to bring it into contact with ordinary matter you would see, not an awesome explosion, but an underwhelming and abrupt nothing.  When exotic matter in brought together with ordinary matter, the positive energy of the matter and the negative energy of the exotic matter cancel out entirely, leaving nothing at all behind.

Exotic matter is a freaking blank check for sci-fi writers.  Warp drives, worm holes, perpetual motion, and even time machines are possible if you allow for negative matter and energy.  In fact, Hawking proved that if you want to build a time machine smaller than the universe, negative energy/mass is a requirement.  Spacetime, as described by general relativity, is pretty limited by the fact that energy and matter seem to be strictly positive.  About the weirdest things you’ll see are black holes, which are pretty cool, but… time machines.  With a liberal peppering of exotic matter (often far more than the universe’s total stockpile of regular matter) you can really open up the flood gates of the weird.

However the big difference, arguably the biggest difference, between anti-matter and negative matter is that negative matter doesn’t exist.

There are some subtle physical laws that imply that the creation of negative energy, in the form of exotic matter or not, has limitations called “quantum interest“.  Anytime a bit of negative energy is generated (and the methods involved create, like, none), a larger, overwhelming pulse of positive energy must be created almost immediately.  In fact, we’ve never directly observed negative energy and it’s very, very likely that we’ll never be able to do more than infer that negative energy exists.

But anti-matter definitely exists, and can be created and stored (a few particles at a time) here on Earth.  Many particle accelerators today generate and use anti-protons all the time.  When you smash stuff together, or otherwise get a mess of energy in one place, new particles are generated; half matter and half anti-matter.  It’s basically annihilation in reverse.  Once you create a spray of new particles, you sort the matter and anti-matter apart, keep the anti-particles ionized, and store them (briefly) in a “magnetic bottle“.  If they ever becomes electrically neutral the magnetic bottle stops working, and they fall and annihilate with the ordinary matter at the bottom of the container.  Anti-particles are totally the hot potatoes of particle physics.

Posted in -- By the Physicist, Particle Physics, Physics | 26 Comments

Q: Why does gravity make some things orbit and some things fall?

Posted on January 30, 2012 by The Physicist

Physicist: This subtlety was one of the great insights of Newton; that the “falling apples” force and the “circling planets” force are one and the same.

Newton's original thought experiment describing the parallels between falling and orbiting. The faster an object moves sideways the longer it stays aloft. Fast enough, and it never hits the ground at all.

Whether gravity pulls an object into orbit or just “makes it fall” depends on how the object is moving.  Basically, every object wants to follow some kind of orbital path.  If you toss a ball, even that ball is following an orbital path.  If that path happens to intersect the ground, then we say “the object fell”.  If that path doesn’t intersect the ground, then we say it’s in orbit.

Anytime an object is in free-fall it's following an orbital path. Gravitationally speaking, until a thing hits the ground it can't tell the difference between the Earth and an Earth's worth of mass crammed into a point (black X).

When in free-fall, all that the ball “knows” is that there’s some gravity around.  When it hits the ground it’s as surprised as anything else.  The path that any tossed or falling object follows is just the tip of a very elliptical orbital path that, if the Earth’s mass were all crammed together in a point, would eventually bring the object back.  Unless you were to throw the ball at a couple thousand mph, it would take about half an hour to complete the loop.

So the only difference between a satellite falling back to Earth and staying in orbit is whether or not the satellite’s orbital path intersects the surface of the Earth.  So, Douglas Adams was right; “Flying is simple. You just throw yourself at the ground and miss.”

Posted in -- By the Physicist, Astronomy, Physics | 15 Comments

Q: Do you need faith to believe in science?

Posted on January 25, 2012 by The Physicist

Mathematician: This question could mean a few different things, depending on what is meant by the word “faith.” Let’s start with the dictionary definitions.

1. Strong belief in God or in the doctrines of a religion, based on spiritual apprehension rather than proof

This has nothing to do with science.

2. Complete trust or confidence in someone or something.

You certainly don’t need complete trust or confidence to believe in the results of science. In fact, this is one of the great things about science: since results can be independently confirmed, you don’t have to trust any individual scientist much at all. In good science, researchers will check each other’s work to see if it holds up, attempting to refute what was claimed by conducting further experiments. And it would be silly to have complete trust in what science has figured out so far. When done right, the process works well at sifting out true ideas from false ones, but even then mistakes will occur which may not be caught for some time. However, when multiple experiments by competent, independent teams confirm a result, we can say that it is very likely to be true (or at least, represent an accurate model of reality).

Sometimes, when people say “science requires faith”, what they are trying to get at is the idea that scientists have to rely on assumptions that they can’t prove. For instance, scientists have to assume that induction works (e.g. that you can generalize about the future laws of the universe by looking at the past laws). If tomorrow the laws of physics were suddenly different than they ever were before, science would be in pretty deep water. The thing is though that all methods for drawing conclusions about the world rely on some hidden assumptions, so saying this is true for science isn’t saying much. In fact, the deep rooted assumptions that science relies on are pretty modest.

When people are able to build working satellites, lasers, bridges and computers using certain methods for acquiring and applying knowledge,  it’s strong evidence that the assumptions made by the methods can’t be that unsound.

Physicist: No.  Exactly no.

In fact having an unshakable belief, even in a particular scientific idea, is detrimental (scientifically speaking).

At the risk of making science sound like the sport of jerks; a good scientist is someone who trusts nothing and no one and is willing to drop their deepest held beliefs as though they were a bucket full of red-hot cobras.  “Science” is nothing more than looking carefully at the world, while trying not to delude or trick ourselves too much, and seeing what’s what.  As a result you find that, unlike conclusions based on faith (which I’m not knocking, good on you if you have them) conclusions based on careful consideration of the world tend to show up independently and frequently.

So while the Conquistadors and Aztecs may have had some subtle differences of opinion about feathered gods and whatnot (who can remember), they already agreed on a lot of stuff involving seasons, water pumps, and astronomy, among other things (though not astrology, oddly enough).

But it’s easy to lose track of all that.  When Sagan says “We are made of star stuff“, as both inspiring and accurate as that is, it still sounds a bit like some kind of ancient creation myth (it also doesn’t help that Sagan was rocking the ’70s vibe).  When you get right down to it, the universe is really weird.

So the claims/findings made by science seem about as crazy as the claims made by everybody else‘s religions (not yours or mine of course): time slows down when you move fast, all matter and energy is made of waves, your mind controls reality*, there are an infinite number of parallel universes**, every living thing is descended from goo or something, the universe is billions of years old, our bodies are made of trillions of semi-independent living things, most of the stuff in the universe is invisible and ghostly, the Earth was once ruled by gigantic monsters that were destroyed by a rock from the sky, the world is really a sphere that’s whipping through an infinite void at hundreds of miles per second while in the company of other spheres some of which are so much larger that Bambi v. Godzilla seems kinda fair, and on and on.

(*Not even remotely true, but you still hear it attributed to “science”.  **This is so misquoted and misunderstood that it’s safer to say that it’s false, but it is something science people say.)

It’s easy to see why science seems like just some wacky new belief system that you have to have faith in to believe.  The difference is, if you don’t believe it (and you’re properly motivated), then you can go out and test it. To be fair, most people do take science on faith.  It’s much harder to test things yourself, than it is to trust that the kind of people who can figure out how to fly around in space and build fancy computers have things pretty well sorted out.  But keep in mind; the option is there.

By the way, here are some fairly interesting, slightly dangerous, things you can test yourself.

Scientists, being a lot like people, have a hard time believing the same weird stuff that bothers everyone else.  I mean, seriously, gigantic monsters?  Something becomes “scientific knowledge” after many people have tried their damnedest to prove it wrong and ended up verifying it instead.

For example, nobody really believed that time slowed down for things that move fast, so (and this was just one of many tests) a couple of dudes put some ridiculously accurate clocks on some airplanes and flew them around to check.  And why would anybody think that we’re made of lots of tiny living things?  If you don’t believe it (and why would you?), get a microscope and a little skin or blood and take a look.  It’s hella gross.

Biology: that’s inside you right now.

Even Schrödinger (of equation, cat, and trance-techno fame) didn’t believe several of the clearly impossible implications of his own equation (like quantum tunneling) until they were experimentally verified.

Some of the more obscure stuff takes a bit more work (money), but at the end of the day when something is “scientific fact” it’s been verified many, many, many times, until the strange and inescapable facts about the universe are forcibly inflicted upon the pitiable scientists who study it.  Science isn’t about making bizarre pronouncements and then having everybody nod sagely and agree on faith.  It’s about making bizarre pronouncements and then throwing it to your colleagues to fall upon and mercilessly tear apart, like ivory tower hyenas.  However, physical reality always has the last word.  If an idea doesn’t stand up to observation and experiment, it’s gone.

Faith is about knowing and certainty, while science is about learning and doubt.  You don’t need either for the other.

Posted in -- By the Mathematician, -- By the Physicist, Philosophical, Skepticism | 30 Comments