## Sunday, February 14, 2016

### Gravity Waves!

Two days ago, on February 11th, the LIGO and Virgo interferometer collaborations announced the first direct observations of gravity waves (actually detected on September 14th, 2015). Why is this a big deal? Gravity waves are one of the predictions of Einstein's general theory of relativity, predicted a hundred years ago in 1916. They were also the last major prediction of general relativity not to have been experimentally verified, and have been the object of search for over fifty years, making this an especially momentous detection.

Gravity waves are caused by the finite speed of propagation of gravity, and are created when any mass accelerates (they're analogous to the electromagnetic radiation emitted by an accelerating charged particle). They're essentially ripples in spacetime, like the wake of a boat on water. However, due to the weakness of gravity, they're very, very weak unless you're talking about extreme concentrations of mass in extremely tiny regions. Thus, the best place to look for them is in binary systems of neutron stars or black holes, and indeed the detected waves most likely came from one of the latter.

You see, all orbiting masses radiate energy away in the form of gravity waves. For most systems, the amount of energy is negligible—for the Earth-Sun system, the radiated energy is about 200 watts; probably less energy than the computer I'm typing this on is using at the moment. The energy lost causes orbiting bodies to move closer together over time, though for the Earth-Sun system the distance works out to about the width of a proton per day (i.e., nothing to worry about). However, for dense masses in close proximity to each other like two orbiting black holes, the amount can be significant enough that it causes the orbits to decay much more rapidly.

Eventually the orbits shrink enough that the two objects (black holes, in this case) merge into a single object. As this happens the frequency of the radiated waves will rapidly rise, then level off in a way that gives a lot of information about the objects involved. In this case, we can say that the two objects were black holes with roughly 36 and 29 times the mass of the Sun, respectively. Unfortunately, due to the fact that only two interferometers actually detected the signal, we can't tell exactly where it came from, merely constrain it to an arc mostly within the South Celestial Hemisphere. It was likely pretty far away though, approximately $$1.3\pm0.6$$ billion light-years away.

There's an interesting feedback effect that happens with this whole process: as the orbits radiate energy away as gravity waves, they shrink, but as they shrink, they radiate more energy away, which causes them to shrink faster, which makes them emit more energy, etc. From the detected signal, it turns out that in the last 20 thousandths of a second before the merger the two black holes were radiating away $$3.6\times10^{49}$$ watts of power as gravity waves; to put that in perspective, that's more energy than is emitted as electromagnetic radiation by all the stars in the observable universe combined. (It really says something about the weakness of gravity that it took this absolutely mind-boggling amount of energy to actually be observable.)

All in all, this was a major step forward in verifying the last major prediction of general relativity, as well as opening up a whole new avenue of investigation for astrophysicists. Now that we know it's possible, hopefully we'll see more work put into additional, more sensitive interferometers in the future that'll allow us to detect weaker gravitational waves from more sources. A hui hou!

## Monday, February 1, 2016

### We Need a SimFarm Remake

Anyone else out there remember playing SimFarm? It was one of Maxis' games from the early-mid 90's, though I didn't get to play it until around the turn of the millennium. Billed as “SimCity's country cousin” it was never as popular as its urban relative, as seen by the way SimCity has had multiple different versions over the years and a successful remake in Cities: Skylines, while SimFarm…hasn't.

And I think that's a shame, because I think there's the seed of a great game in SimFarm just waiting for an updated and modernized remake to bring it out. For those who haven't played it, SimFarm casts you as the owner of a small plot of land, empty but for your cozy little farm house and just waiting for you to develop it into a thriving family farm. Farming happens from a bird's-eye perspective where you oversee your various fields and animals. The weather changes over the course of an in-game year, and the climate of your starting area (you get to pick your location on a map of the lower forty-eight states at the start of the game) affects how well various crops do (apples do well in Washington, sunflowers in Kansas, etc.).

There a number of natural disasters that can happen at random, such as tornadoes, floods, and plagues of locusts, all of which can affect your farm in different ways. Somewhere on the map there's a small town, which periodically expands with different types of districts, some of which can also affect your farm (getting a fairground allows you to enter animals in competitions at the fair, and the airport allows you to buy and use cropdusters). Success in the game consists of managing your farm well (whether crops or animals) in such a way as to turn a profit, which allows you to buy additional land and expand your farm further.

All in all it was a fun experience (at least to my ~10-year-old self), and one that isn't really replicated in any game I'm aware of (please enlighten me if one exists!). To forestall potential criticism, I'm aware that there are games that play on similar themes. Probably the biggest and most famous is Farming Simulator 2015. Unlike SimFarm, however, Farming Simulator 2015 is operated in first-person mode with the player manually controlling various pieces of equipment. SimFarm, in contrast, has the player simply ordering things to be done (such as planting or harvesting a field), and the appropriate equipment springs into action if available (presumably piloted by invisible family or farm hands). Farming Simulator 2015 also uses pre-built maps that can't really be meaningfully changed, while a lot of SimFarm's charm comes from the way you can rearrange the map the way you see fit to build your dream farm.

I mentioned SimCity earlier, because I wanted to mention its 2015 remake Cities: Skylines by developer Colossal Order. The latest SimCity sequel (usually known as SimCity 2013) was widely panned by critics and players alike, and the people at Colossal Order decided to take it upon themselves to create a SimCity-like game from the ground up. The fruit of their efforts was Cities: Skylines, a critically-acclaimed, updated and modernized city-building game making full use of the many advances in the years since the original it was based on came out. I recount this to show what I'd like to see for SimFarm: someone to create a similar-but-modernized game from the ground up for today's audience taking advantage of today's technology. I'm not in a position to make one myself, but hey, maybe Colossal Order is taking suggestions on what to make next…