To Boldly Go Where No Head Has Ached Before

Space travel is a bit of a headache. Actually, that's underselling the problem, space travel is an enormous headache. There are so many things that can go wrong and so many things that need to be accounted for to keep astronauts safe in a cruelly punishing environment. You have to think about air, radiation, the lack of gravity ... the list goes on and on.

And now, if the metaphorical headaches weren't bad enough, astronauts also need to contend with the actual headaches. 

In research published in Neurology, 22 of 24 astronauts followed during a 7-year period of observation on the International Space Station experienced one or more instances of headache, with 378 headaches being reported over 3,596 total days in space. In addition, before going into space, only 38% of those astronauts experienced headaches; after returning to Earth, no astronaut reported experiencing headaches.

It's perhaps not surprising that headaches were worse during the first week in space, being both worse in severity and more likely to be migraine-like, but headaches continued to occur throughout each astronaut's time in space.

So, what's going on to make space both a figurative and literal headache? While the study authors stressed that the study findings only show an association between space travel and headaches, they added that it most likely comes down to the lack of gravity. Not only does zero G degrade your bones and muscles, it also affects balance and posture. Space motion sickness is extremely common, and while vomiting may be the first thing that comes to mind for astronauts who haven't gotten their space legs yet, headache is actually just a common a symptom of motion sickness.

Now obviously, there are bigger problems to tackle than space headaches when it comes to making human space travel possible. Still, it is an important issue to tackle. We don't want the first person to step foot on Mars to walk out of the lander and say "that's one small step for man, one giant leap for the ibuprofen keeping the migraines at bay."

The Good News For General Relativity Keeps On Coming

Not too long ago, I wrote about how alternate theories to general relativity have been having a tough time as of late. Well, things just got even tougher.

The equivalence principle was on trial for this experiment. One of the basic tenets of relativity is that two objects, no matter what their mass or what they're made of, they are affected by gravity in the same way. This has been tested many times on Earth (and famously, on the Moon), but never with really dense objects. Alternative theories to relativity assume that the equivalence principle breaks down at high density, since up to now, there's been room to work.

The test involved  a neutron star-white dwarf pair, and watching the orbit of the neutron star. If there were variations in its orbit, it would have been in violation of the equivalence principle, and the various alternate theories would have some ground to stand on. But there was no variation, and once again, general relativity was proven correct. And not only that, but this test improved the accuracy of the previous best gravity test by a factor of 10. Alternate gravity theories thus have a lot less room to work.

Alternate Theories to Relativity Have Not Had a Good Time Lately

It's a conundrum at the very heart of theoretical physics. We know quantum mechanics to be correct. It's how nature works at very small scales. We know that the theory of general relativity is completely incompatible with quantum mechanics. The two just don't go together. Therefore general relativity must be wrong, or at minimum, incomplete. Yet general relativity has been proven to work time and time again. But general relativity also means that dark matter and dark energy must be a thing. And despite our best efforts, we're no closer to discovering either than when we first started looking for them. Not really. And I think you get the idea at this point. It's a mess.

So, what are physicists to do? If you guessed make wild theories that somehow work in what we know about gravity AND what we know about quantum mechanics, and hope the two go together, then congratulations! You've got what it takes to be a theoretical physicist. Turns out there are lots of alternate theories of gravity out. Well, there were. The discovery of gravitational waves by LIGO killed most of them. Okay, it wasn't just that, it was that and the simultaneous observation of a gamma-ray burst from the same neutron star collision.

I think the biggest takeaway from this story is that science is always in motion. General relativity's been around for a century now, and it's been observationally validated many, many times. But it isn't perfect. And so, rather than shrug our shoulders and say "close enough", we keep going, and we try to find something that does work. There is always more science to do, always more questions to answer.

Discovery of Gravitational Waves Announced

It really doesn't sound like very much, does it? The existence of gravitational waves, first theorized by Albert Einstein, is accepted by pretty much everyone. But for the past 100 years, we've never been able to detect them. We've tried, but gravity, as it turns out, is ridiculously weak.

Perfect, now just stuff that in a water bottle

Let's do a little comparison between gravity and the other 3 fundamental forces, just to demonstrate gravity's weakness. Imagine the force of gravity represented as a 1 kilogram object sitting on a table. A big bottle of water that holds 1 liter weighs a kilogram, if you need a visualization. It's not a problem to pick up, right? Everyone can pick up a bottle of water. That bottle represents gravity's comparative force. Now, let's replace gravity with a similarly sized bottle with the comparative weight of the weak nuclear force, the next weakest fundamental force. That bottle, previously 1 kilogram now weighs nearly as much as Earth and Venus combined. It would then turn into a black hole. As it turns out, the weak nuclear force is stronger than gravity by a factor of 1 * 10²⁵. Try picking that up.

The story only gets worse with the other 2 forces. Let's move on to electromagnetism, which along with gravity is the fundamental force we all know. It's stronger than gravity by a factor of 1 * 10³⁶. For reference, the Sun weighs about 2 * 10³⁰ kg. Our bottle would weigh about as much as 500,000 Suns. This is nearly as heavy as Segue 2, a dwarf galaxy and Milky Way satellite which is (according to Wikipedia) the least massive galaxy known; but far, far more than the most massive stars, which weigh in at around 200-250 solar masses. Again, it would then become a black hole. The strong nuclear force is only 100 times stronger than electromagnetism, so our bottle now weighs 50 million solar masses. For comparison, the supermassive black hole at the center of the Milky Way is only about 4.5 million solar masses. At that mass, our bottle actually would not become a black hole...yes it would.

Credit: LIGO

It would clearly be no easy task then to detect gravitational waves. But today, scientists with the Laser Interferometer Gravitational-Wave Observatory announced that they had finally managed to do it. The project used a pair of detectors 2,000 miles apart to detect the waves, which compress a laser in one arm of a detector and stretch the laser of the other arm. 2 detectors are necessary to confirm the result, and to triangulate the location of the gravitational wave. It's an incredibly sensitive experiment, but it has to be. Even the largest gravitational waves, emanating from sources such as supernovas and black hole collisions, cause a change in laser length measured at the subatomic level.

On one hand, this isn't exactly the most exciting news. Gravitational waves have been observed indirectly before, and like I said before, very few doubted that they existed. But on the other hand, direct observation is a lot better than indirect. While we can't rule out an error in the experiment (and verifying this observation will be very difficult, since LIGO is the only detector powerful enough to detect gravitational waves), it seems that this announcement will likely be the real deal. It represents a powerful confirmation of general relativity, and now that we know how to detect gravitational waves, we can take the process further, learning much more about the universe. It really is a bigger deal than it sounds.