Swedish Scientist Suggests That There Is Only One Earth (blastingnews.com)

MarkWhittington writes: The conventional wisdom has been among scientists is that a myriad of Earth-like planets exist in the universe, some of which have to be the abode of life, even intelligent life. However, Astrophysicist Erik Zackrisson from Uppsala University in Sweden has run a computer simulation of the universe, incorporating what we know about exoplanets thanks to the Kepler Space Telescope, the laws of physics, and the state of the early universe. The computer simulation came up with exactly one Earth, which is to say the one we live on. Every other planet in the universe does not have the conditions necessary to sustain life. Indeed, strictly speaking, Earth itself should not exist, according to the computer model, according to the story in Discover Magazine.

Comments

If accurate, this is good news. But be skeptical

[JoshuaZ]

If this is accurate this is good news. One of the standard explanations for the Fermi Paradox is that Earth-like planets are very rare https://en.wikipedia.org/wiki/Rare_Earth_hypothesis. You may ask why this is good news? The reason is that something is making civilizations rare. We don't see any signs of major civilizations, either in terms of visits, radio waves, or most importantly, megastructures and large-scale engineering projects. At this point, we've looked at 100,000 nearby galaxies and essentially none of them show signs of a highly advanced civilization in terms of energy use http://www.universetoday.com/119931/100000-galaxies-and-no-obvious-signs-of-life/.

The standard explanation for this is that there is some "Great Filter" which is making civlizations rare https://en.wikipedia.org/wiki/Great_Filter. If this is something in our past (e.g. habitable planets are rare, it is tough for life to evolve, it is hard to get those last few steps to necessary levels of intelligence, etc.) then we don't need to worry. But if it is something in our future, something that civilizations do to wipe themselves(e.g. nuclear war, bad nanotech) out then we're in trouble. We need to figure this out soon, since if there is a future Filter then it likely occurs very close to our current tech level.

Every piece of evidence for early filters should make us breathe more easily since it makes late filters less necessary. Unfortunately in the last few years, almost all new evidence has been in the other direction: we've found lots of planets and it looks like even small, rocky planets are common. So this is a refreshing piece of news. However, I'm very skeptical of it. First, it seems to go against other similar studies suggesting that as many as 1/3rd of stars may have an Earth-like planet (see e.g. here http://www.universetoday.com/119931/100000-galaxies-and-no-obvious-signs-of-life/) and they appear in order to be getting this result in part to be using an extremely narrow notion of what a habitable planet would look like.

Re:Then he's doing it wrong.

[Jason Levine]

If I recall correctly, we don't yet have the capability to detect Earth sized planets. They are just barely out of our detection range. However, when we were able to detect super-Jupiter sized planets, we found a lot of them. As our detection size shrinks, the number of planets found keeps growing. If this holds up, then in when we finally get down to being able to detect Earth-sized planets, things could get interesting.

Of course, then there are moons. Imagine a solar system like our own, but with Jupiter where we are. Jupiter wouldn't be habitable, but Europa might be. A large moon orbiting a gas giant might be able to sustain life and all we'd see from here (at the moment) is "gas giant in the habitable zone, move on."

Re:Then he's doing it wrong.

[hey!]

Well, a lot of the language we're using to talk about this is unsatisfyingly vague. What does it mean that "the Earth should not exist"? And especially "strictly speaking"; people misuse that phrase the way they misuse "literally" -- i.e. to mean exactly the opposite of what it actually does.

If the model strictly speaking precludes the existence of the Earth, then the model was constructed wrongly. But what if the model simply predicts that the most likely number of Earth-like planets is zero? That would not, strictly speaking, preclude the Earth existing. Presumably the next most likely number of Earths would be one, followed by two etc.

In any case I have some experience with models of complex systems about which data is somewhat spotty -- in my case zoonotic diseases, which depend on all kinds of things which we don't have very good data about. So we run them with suppositions, which we dignify by calling "parameters". The thing about such models is that they're mainly useful in generating research questions than making predictions. We might not know exactly how quickly a virus amplifies inside a disease vector like a mosquito; if the model suggests that human transmissions go up rapidly with shorter amplification times, then that becomes a research priority. It can't tell you that if zika virus establishes itself in Miami this year that we'll get 22 cases.

It seems to me that we're at an analogous place with models of exosolar planets. We've only been detecting them for a few years, so while it's a reasonable starting point to assume that they're representative of planets in the universe as a whole, that isn't necessarily true. Indeed it's possible we'll never be able to observe a representative sample of planets.