During Neil deGrasse Tyson’s talk on Tuesday, he talked about firing photons one at a time to produce a result.  During almost any talk about physics experiments you will eventually hear about physicists shooting individual photons.  Despite its near ubiquity and my hundreds of hours of physics classes I’ve never really heard an explanation of how physicists manage to produce a single photon.  None of my friends had either.  So I decided to hit the interwebs and find an answer.  It is so simple, I am almost ashamed that I didn’t come up with an explanation on my own.  More proof that my brain is slowly turning to mush from lack of exercise.

Think about a flashlight.  Turn it on and light goes beaming out.  That light is composed of untold schmillions of photons.  Electricity is running through the filament causing the (usually) tungsten filament to heat up and produce light.  The electrons passing through the tungsten will collide with an individual atom temporarily causing the individual atom’s outer shell electron to jump to a higher energy level.  This is an unstable condition for the atom so the electron will eventually fall back down and photons will be produced.

“But that doesn’t help us, we still have multiple photons being produced!”, you might exclaim.  And you’d be right.  Here’s where a little ingenuity is involved.  We need a source which produces a known number of photons at known wavelengths.  Enter the spectrometer!  Thanks to that lovely invention, we know the wavelengths of the photons produced for just about everything.  Prior to that, I assume it was mostly trial and error.

Now it’s just a matter of choosing a substance, isolating it, and running just enough electricity through it to produce a reaction on a single atom.  But what shall we choose?  It turns out there are plenty, but the easiest example I could find is sodium.  A single sodium atom produces two distinct wavelengths of light at 588.9950 nm and 589.5924 nm.  Oops, but that’s still two photons, what do we do now?  Filters!  We just place a filter across the path of the photons that blocks one of the wavelengths and voila, a single photon source!

Obviously, creating a device capable of firing a controlled amount of electricity across a controlled number of atoms is non-trivial, but that’s the basic concept.  You just take your basic light source and winnow it down to its atomic level.

Once upon a time, there was a blast of neutrinos detected on Earth, followed three hours later by another blast of neutrinos.  7.7 hours after the initial blast, a star brightened in the tell-tale signs of a supernova in the Large Magellanic Cloud.  This is highly unusual because neutrinos and photons both travel at the speed of light and while it is known that photons spend the first 3 or so hours bouncing around inside a supernova, there’s still 4.7 hours unaccounted for.  Since scientists couldn’t explain the arrival time difference, they dismissed it as two separate occurrences even though the probability of them being related is quite high.

Now, scientists have a mathematical solution for the time difference.  Basically, it goes like this.  Neutrinos for the most part do not interact with matter at all.  They can go right through the Earth as if it were empty space.  Photons are not so lucky.  They can be bent by gravity, they can run into matter, and they can cease to be photons for miniscule moments of time to form an electron-positron pair.  The latter is where things get interesting.  An electron-positron pair suddenly has mass that can be much more affected by gravity than a lone photon.  It last for no time at all before going back to a photon, but scientists found that this new gravitational potential of the electron-positron pair corresponds to the missing 4.7 hours.

This is fascinating because a quantum mechanical effect has been combined with a relativistic effect to produce a result.  If this explanation for the missing 4.7 hours is correct, could this discovery lead us down the path of other discoveries that will lead to a unified field theory?  I also wonder what this means for our calculations of distances of objects.  If the Large Magellanic Cloud is 4.7 light hours farther away than previously thought at 160,000 light years distance, how much farther away is UDFj-39546284 at 13,370,000,000 distance?  What if the effect isn’t linear?

You ever wonder why pet mice and gerbils and such seem to enjoy those little exercise wheels so much?  Probably because they are in this little cage and there’s not much else to do, right?

Wrong.

Scientists decided to take exercise wheels out of the cages and put them in places outside and see what would happen.  One they put in a green urban center and another they put in a remote dune area.  Much to their chagrin, they found that wild mice and rats and even some snails, slugs, and frogs enjoyed using the exercise wheel.  Over three years, they recorded over 1,200 uses of the exercise wheel.  They originally used food to lure the animals to the exercise wheel site, but on the chance that they were using the wheel because of the food, they removed it and still were recording wheel usage.

This is the kind of experiment that gets mocked by people who don’t have a basic understanding of how science works.  I have no idea if there are any useful scientific conclusions to draw from this experimeint or not.  The authors suggest that there may be something to gleen about the habits of sedentary versus more active humans, but who know.  They did an experiment that was never attempted before and reached a conclusion that is at least somewhat unexpected.  Basic science like this is how big discoveries are made.  There is a quote that I remember, but can’t find the source and it goes something like this: Great discoveries are often thought to come from someone burning the midnight oil and coming across some new discovery and shouting “Eureka!”, but more often than not it comes from someone looking at a bit of gathered data and thinking to herself, “That’s odd”.

You know how Pompeii was destroyed in an instant from the eruption of Mt. Vesuvius?  What did all of the damage and the amazing preservation is what’s called a pyroclastic flow.  It’s a very fast-moving conglomeration of ash and gasses and lava that has immense destructive powers.  It’s one of those things that happens so quickly, you don’t have much time to document it.  Luckily, scientists are getting a lot better at predicting volcanic explosion so there’s usually a camera or ten around to capture the awesomeness.  Here is an example of said awesomeness:

There is some more promising great news in the quest for cheap, renewable fuel front.  The Pacific Northwest National Laboratory is licensing a process that can create oil from an algae slurry in an hour and the company, Genifuel, is starting production on an industrial scale machine to produce it.  Even better, the byproducts of this process are all recyclable.  Unfortunately, the produced oil then needs to go through the normal refining process to create gasoline, etc. which is horribly polluting, but that environmental damage can at least be limited to a small geographic area as opposed to the drilling for oil which all to often has vast implications on large swaths of land.

Of course, this still leaves us in the same boat of burning gasoline to power our cars and I’m not sure that’s a tenable solution for the long run.  It also still remains to be seen if this process can be expanded to the scale of our voracious appetite for oil.  Regardless, it’s a tantalizing look into what could be our solution to our dependence on foreign oil.