No Man's Sky versus the actual universe: a scientific inquiry

Thanks to the steady drip-feed of information and videos from Hello Games HQ, we now know exactly how big No Man’s Sky will be, and we have a fair idea of how it’s possible to create such a huge universe through procedural generation. (We’ve also seen how impressively big Sean Murray’s beard has got over the past year – we presume he’s growing it as some kind of metaphor to indicate the increasing extravagance of the project.)

Related: I played No Man’s Sky with an astronomer to separate its science fiction from facts

We know that you can explore billions upon billions of planets and find some kind of life on a decent proportion of them. But how big is No Man’s Sky compared to the real Universe? What are the actual chances of finding extraterrestrial life? And what would alien life look like anyway?

Galactic map in No Man’s Sky. Eeeeeeeeeeeeeee, it’s big.

How big is No Man’s Sky compared with the actual Universe?

According to Hello Games, there are 18 quintillion planets to explore in No Man’s Sky (or 18,446,744,073,709,551,616 to be exact), which is an obscenely large number. To put that in perspective, if you visited each planet for a single second, it would take 585 billion years to see them all. Sean Murray reckons that “99.9% of the planets will probably never be visited”. The star map at the end of the video below gives a glimpse of the game’s enormity.

But how does this absurdly large figure compare with the number of planets in the real Universe? We can only guess at the actual number of planets – after all, scientists only confirmed the existence of exoplanets (planets outside our Solar System) in the early 1990s. Since then, the Kepler space observatory has found more than 2,000 exoplanets - and those are just the ones that happen to cross in front of their parent star in Kepler’s plane of view. In reality, there are likely to be many, many more planets even in the small patch of sky that Kepler is looking at, but we currently don’t have the technology to see them.

Then there are all of the orphan planets, or ‘rogue planets’, that wander between the stars. These shadowy beasts are devilishly tricky to spot or analyze because there is no nearby light source to illuminate them, and the first potential orphan planet was only observed in 2004. Since then, only a handful of rogue-planet candidates have been discovered, but there could be billions of them in our galaxy alone.

Based on the current data, astronomers reckon that on average there is one planet for every star in our galaxy, the Milky Way. There are at least 100 billion stars in the Milky Way (but various estimates also put this figure at 400 billion or much higher), so we have at least that number of planets in our galaxy, and possibly more.

At this point, the scale of the known Universe really tap dances across the line into astounding. In the early 2000s, the Hubble space telescope pointed its lens at a seemingly ‘empty’ patch of sky (to the naked eye at least) for a total of 11 days to gather even the faintest scraps of light from the most distant stars. The image it produced, known as the ‘Hubble Ultra-Deep Field’, shows that the Universe is absolutely teeming with galaxies for as far as we can see.

Hubble Ultra-Deep Field.

A follow-up image known as the Hubble eXtreme Deep Field was produced in 2012, in which the telescope was focused on the same square of sky for even longer - 23 days. The result was an image showing even more galaxies right up to the edge of the observable Universe. The light from the most distant ones took 13.2 billion years to reach us.

Based on just the most conservative estimates, there are at least 200 billion galaxies. That means, in terms of the number of stars in the observable Universe, we’re looking at around 10 to the power of 22 or 24. And if other galaxies are similar to our own, that means there will be a similar number of planets. In other words, around 1,000,000,000,000,000,000,000,000 other worlds.

That’s a good five digits longer than the number of planets in No Man’s Sky, but considering that No Man’s Sky is a video game made by a handful of people, it’s astonishing that the number even comes close.

How similar are the planets in No Man’s Sky to real exoplanets?

No Man’s Sky takes a few liberties with reality when it comes to representing planets. The developers decided to make all of the planets in the game explorable, so you can land on the surface and wander about to your heart’s content. Some have extremely low or high temperatures, or toxic atmospheres, but nothing to stop the determined wanderer with a suitably beefed-up spacesuit.

You can walk on the surface of all of No Man’s Sky’s planets – unlike in the real Universe.

However, in real life, not all planets are so accommodating. For a start, a significant number of exoplanets are gas giants, like Jupiter and Saturn, which are mainly composed of hydrogen and helium and don’t have a solid surface. Not only that, many of the first exoplanets to be found were so-called ‘hot Jupiters’, a class of planet unlike anything in our own Solar System. They’re huge, up to nearly 12 times the size of Jupiter, but they orbit incredibly close to their parent star - some are so close and orbit so fast that their ‘year’ lasts only 1.3 days. The night side of a hot Jupiter can be hundreds of degrees cooler than the day side, which contributes to extreme winds that whip around the planet at phenomenal speed.

And of course, there are the rogue planets I mentioned earlier, which don’t even have a parent star. Travelling through the voids of space, these orphaned planets would have a pitch black surface and be extremely cold.

Having said that, most of the planets discovered so far are between the size of Earth and the ice giant Neptune, with many falling into the class of ‘Super Earth’. No equivalent size of planet exists in our Solar System, but in general the larger the planet, the less likely it is to be rocky - and the more likely it is to consist of volatile chemicals and gas.

How easy is it to get to the nearest exoplanet?

Space travel in No Man’s Sky is enviably easy. You can effortlessly take off and reach the top of a planet’s atmosphere in seconds, then hyperjump to another planet in an instant. See the vid below to get an idea of what I mean.

In the real Universe, it’s not quite that simple, of course. It takes an enormous amount of energy just to escape Earth’s gravity; NASA’s Space Shuttle carried nearly half a million kilograms of solid fuel in each of its two rocket boosters, plus nearly two million litres of liquid fuel in its external tank. And that’s just to get into Earth orbit and stay there, never mind travelling to another planet.

Hyperdrives are very much in the realm of science fiction, although interestingly there is talk of a possible way to make a warp drive by manipulating spacetime. Wormholes are another possibility for faster-than-light travel - they’re allowed by Einstein’s Theory of General Relativity (although no-one has ever seen one), and if you could harness the gigantic amounts of energy required to create one, you might be able to use it to take a shortcut to another part of the galaxy. Although you’d have to figure out some way to point it in the right direction.

But assuming that hyperdrives and wormholes are unavailable, we’re limited by the speed of light. That means that the nearest exoplanet to Earth, which is orbiting Alpha Centauri B, would take 4.3 years to reach if we could travel at lightspeed.

We’re a long way off doing that though. The fastest ever spaceship was NASA’s Juno mission, which got up to 40,000 meters per second after doing a slingshot around the Sun. That sounds impressive until you realize it’s just 0.013% of the speed of light, which travels at 299,792,458 meters per second.

What is the actual likelihood of encountering aliens on a planet?

Most of the planets in No Man’s Sky will be barren of life. Only a relative few will be densely packed with plants and animals - but even so, life will be fairly common in the game. How representative is this of the distribution of life in the actual Universe?

How common is this scene across the Universe?

The obvious answer is: we don’t know. We’ve only ever found life on one planet, and that’s our own. It’s very hard to extrapolate from a sample of one.

But the fact that we’ve so far only found life on one planet in our Solar System seems to indicate that it’s a pretty rare occurrence. More importantly, the fact that we haven’t detected any signals from alien civilizations - or been visited by them - perhaps indicates that they’re not out there at all.

The sheer number of stars and planets in the Universe would make it seem logical that life – and indeed advanced civilizations – have had the right conditions to evolve many, many times. The famous Drake equation even gives a formula for calculating how many civilizations there are around us - possibly 100,000 in our galaxy alone, depending on the variables you enter. But the Drake equation in turn gave rise to the Fermi paradox: if there’s such a high probability of advanced civilizations existing just around the corner in galactic terms, why haven’t we heard from them?

There are several possible answers to the paradox (which are wonderfully explained by the excellent Wait But Why). One is the Rare Earth Hypothesis, which states that Earth really is incredibly unique, and we’re perhaps the only civilization that has survived this far. Pretty depressing stuff - and it makes the vibrant colonies and space stations of No Man’s Sky seem far-fetched. Another possibility is that conditions in the galaxy have only just reached the point where it’s possible for civilizations to survive long enough to contact each other, so there are thousands of alien races out there that are just on the cusp of being able to contact us.

Yet another possibility is that the aliens are out there, but they just don’t want to talk to us because we’re too primitive. This is known as the Zoo Hypothesis – and it’s basically the Prime Directive from Star Trek.

A scarier possibility is that other alien civilizations are out there, but we can’t detect them because they’re hiding from some sort of malevolent, all-powerful conqueror race - which makes our naive efforts to send ‘hello’ signals to the stars seem downright foolish. In fact, cosmologist Stephen Hawking reckons that we should go out of our way to avoid contacting aliens, as it’s unlikely to end well: “If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans.”

If we did meet aliens, it might be in the form of von Neumann probes sent out by them - self-replicating probes that can explore planets and star systems, and make copies of themselves using the resources they find. In this way the number of probes would increase exponentially, and they would quickly spread throughout the galaxy. The fact that we haven’t encountered any indicates either that there are no aliens out there or that creating von Neumann probes is a fundamentally bad idea, as if left unchecked they would eventually consume all of the mass in the galaxy. Still, in an interesting parallel, Hello Games actually created their own probes to send out into the No Man’s Sky universe - they’re out there now, beaming back animated gifs of the planets they find to their creators.

But putting the Fermi paradox to one side for a minute, it seems like a fair bet that life has evolved many, many times across the galaxy - an assumption that’s supported by the recent finding that habitable planets are actually fairly common. There are at least 132 habitable planets in our stellar neighborhood alone (within 33 light years of the Sun). But that figure is assuming that life evolved elsewhere in the same way that it did on Earth - which brings me on to...

What would aliens actually look like?

In No Man’s Sky, the creatures we’ve seen in gameplay footage so far seem to follow many of the basic templates found on Earth. We have animals that resemble dinosaurs, fish, lions, antelope – they may look exotic, but they’re also familiar. A few have no obvious analogue, like the kite-like fish things floating through the air, but we can still recognize traits from Earth animals, like jellyfish or eels.

I’m going to call these things Streamer Eels.

Some people argue that this is spot on. Professor Simon Conway Morris argues that human-like alien creatures have probably evolved many times as a result of convergent evolution. In other words, nature comes up with the same solution to the same problem by different routes, as we see on Earth in the way that the eye has evolved independently many times in many different evolutionary lineages. So alien analogues of terrestrial species are to be expected.

But this assumes that alien life faces similar conditions to life on Earth. Undoubtedly, many Earth-like planets do exist. But on planets with crushingly heavy atmospheres or extreme gravity, we might see the evolution of much more horizontal, squat creatures. Likewise, creatures on lighter planets could be tall and spindly.

It seems a fair bet that alien creatures will exhibit bilateral symmetry – that is, one half of their body is a mirror image of the other half – as this trait is universal on Earth and is seen in inanimate objects such as crystals. But would they have DNA? Some argue yes, seeing as this chemical is inseparable from life on Earth. But others suggest that alien life forms could easily be based on silicon or even iron rather than carbon - and even that life could have evolved in ways that we can barely comprehend. Sci-fi author Aaron Rosenberg argues:

“Perhaps life on other planets evolved without physical form or with no fixed form—perhaps there are aliens who are nothing more than sentient clouds, or who have mutable bodies that can alter to suit the needs of the moment. Maybe they can sail through space unaided, and use stellar radiation for a food source and a sensory array, detecting changes in the radiation the same way bats detect sound waves. Who needs eyes and ears when your entire being resonates? Who needs a distinct brain when your consciousness is spread throughout just like our nerve endings are with us? Why have skin when your form is held together by electrostatic shock and mental control, and can condense or expand at will?”

Comparison of Earth and Gliese 581c, the first terrestrial planet to be discovered in a star’s habitable zone.

It’s also worth noting that astronomers who are hunting for ‘habitable’ planets have focused on the ‘Goldilocks Zone’ - planets that are just far away enough from their star to have liquid water, as opposed to ice or water vapor. Water is essential for life on Earth because it acts a a universal solvent, a medium in which the reactions of life can take place - but some have suggested that other mediums, such as liquid methane, could do the job just as well, which means that life could even exist on colder planets that we initially deemed uninhabitable.

So perhaps there IS plenty of life out there, even if there seems to be no sign of other advanced civilizations. The downside is that, just like on Earth, the vast majority of it will consist of single-celled organisms.

Still, planet after planet populated with nothing but microorganisms would make for a helluva dull video game - it may be less ‘accurate’, but I’m glad that Hello Games has focused more on space dinosaurs than single cells. Roll on 24th June.

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