Stephen Hawking on the Possibility of Non-Carbon-Based Extraterrestrial Life

On the 50th anniversary of NASA, Stephen Hawking, Newton's heir as the Lucasian Professor of Mathematics at the University of Cambridge, was asked the question, “Are we alone?”

His answer was short and simple; "probably not."

Hawking outlined three possibilities. One, being that there is no life out there, and two – somewhat pessimistically, that when intelligent life gets smart enough to send signals in to space, it is also busying itself with stockpiling nuclear bombs.

Hawking, known not only for his sharp mind, but his also for his biting sense of humor, prefers option number three. "Primitive life is very common and intelligent life is fairly rare," he quickly added: "Some would say it has yet to occur on earth."

We should be careful if we ever happen upon extraterrestrial life, Hawking warns. Alien life may not have DNA like ours: "Watch out if you would meet an alien. You could be infected with a disease with which you have no resistance."

What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous, Hawking observed in his lecture, Life in the Universe. We can imagine  that one might have life with some other chemical basis, such as silicon, "but carbon seems the most favorable case, because it has the richest chemistry."

The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, Hawking observes, "some of these atoms came to be arranged in the form of molecules of DNA. One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated."

Other prominent scientists have warned that we humans may be blinded by our familiarity with carbon and Earth-like conditions. In other words, what we’re looking for may not even lie in our version of a “sweet spot”. After all, even here on Earth, one species “sweet spot” is another species worst nightmare. In any case, it is not beyond the realm of feasibility that our first encounter with extraterrestrial life will not be a solely carbon-based fete.

Alternative biochemists speculate that there are several atoms and solvents that could potentially spawn life. Because carbon has worked for the conditions on Earth, we speculate that the same must be true throughout the universe. In reality, there are many elements that could potentially do the trick. Even counter-intuitive elements such as arsenic may be capable of supporting life under the right conditions. Even on Earth some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines.

Several other small life forms use arsenic to generate energy and facilitate growth. Chlorine and sulfur are also possible elemental replacements for carbon. Sulfur is capably of forming long-chain molecules like carbon. Some terrestrial bacteria have already been discovered to survive on sulfur rather than oxygen, by reducing sulfur to hydrogen sulfide.

Nitrogen and phosphorus could also potentially form biochemical molecules. Phosphorus is similar to carbon in that it can form long chain molecules on its own, which would conceivably allow for formation of complex macromolecules. When combined with nitrogen, it can create quite a wide range of molecules, including rings.

So what about water? Isn’t at least water essential to life?

Not necessarily. Ammonia, for example, has many of the same properties as water. An ammonia or ammonia-water mixture stays liquid at much colder temperatures than plain water. Such biochemistries may exist outside the conventional water-based "habitability zone". One example of such a location would be right here in our own solar system on Saturn's largest moon Titan.

Hydrogen fluoride methanol, hydrogen sulfide, hydrogen chloride, and formamide have all been suggested as suitable solvents that could theoretically support alternative biochemistry. All of these “water replacements” have pros and cons when considered in our terrestrial environment. What needs to be considered is that with a radically different environment, comes radically different reactions. Water and carbon might be the very last things capable of supporting life in some extreme planetary conditions.

Posted by Casey Kazan with Rebecca Sato.

This is the fourth and final post in a four-part series on Stephen Hawking's views on life in the universe.

Related Galaxy posts:

Stephen Hawking: Why Isn't the Milky Way "Crawling With Self-Designing Mechanical or Biological Life?"

Stephen Hawking: "Humans Have Entered a New Stage of Evolution"
Stephen Hawking: "Asteroid Impacts Biggest Threat to Intelligent Life in the Galaxy"

MIT Asks: How Would Extraterrestrial Astronomers Study Earth?
"The Great Silence" -A Galaxy Insight
Harvard-Smithsonian Scientists Zero In On Key Sign of Habitable Worlds

Sources:

http://www.rationalvedanta.net/node/131

http://www.physorg.com/news128057557.html

Hawking, known not only for his sharp mind, but his also for his biting sense of humor, prefers option number three. "Primitive life is very common and intelligent life is fairly rare," he quickly added: "Some would say it has yet to occur on earth."

We should be careful if we ever happen upon extraterrestrial life, Hawking warns. Alien life may not have DNA like ours: "Watch out if you would meet an alien. You could be infected with a disease with which you have no resistance."

What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorous, Hawking observed in his lecture, Life in the Universe. We can imagine  that one might have life with some other chemical basis, such as silicon, "but carbon seems the most favorable case, because it has the richest chemistry."

The Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, Hawking observes, "some of these atoms came to be arranged in the form of molecules of DNA. One possibility is that the formation of something like DNA, which could reproduce itself, is extremely unlikely. However, in a universe with a very large, or infinite, number of stars, one would expect it to occur in a few stellar systems, but they would be very widely separated."

Other prominent scientists have warned that we humans may be blinded by our familiarity with carbon and Earth-like conditions. In other words, what we’re looking for may not even lie in our version of a “sweet spot”. After all, even here on Earth, one species “sweet spot” is another species worst nightmare. In any case, it is not beyond the realm of feasibility that our first encounter with extraterrestrial life will not be a solely carbon-based fete.

Alternative biochemists speculate that there are several atoms and solvents that could potentially spawn life. Because carbon has worked for the conditions on Earth, we speculate that the same must be true throughout the universe. In reality, there are many elements that could potentially do the trick. Even counter-intuitive elements such as arsenic may be capable of supporting life under the right conditions. Even on Earth some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines.

Several other small life forms use arsenic to generate energy and facilitate growth. Chlorine and sulfur are also possible elemental replacements for carbon. Sulfur is capably of forming long-chain molecules like carbon. Some terrestrial bacteria have already been discovered to survive on sulfur rather than oxygen, by reducing sulfur to hydrogen sulfide.

Nitrogen and phosphorus could also potentially form biochemical molecules. Phosphorus is similar to carbon in that it can form long chain molecules on its own, which would conceivably allow for formation of complex macromolecules. When combined with nitrogen, it can create quite a wide range of molecules, including rings.

So what about water? Isn’t at least water essential to life?

Not necessarily. Ammonia, for example, has many of the same properties as water. An ammonia or ammonia-water mixture stays liquid at much colder temperatures than plain water. Such biochemistries may exist outside the conventional water-based "habitability zone". One example of such a location would be right here in our own solar system on Saturn's largest moon Titan.

Hydrogen fluoride methanol, hydrogen sulfide, hydrogen chloride, and formamide have all been suggested as suitable solvents that could theoretically support alternative biochemistry. All of these “water replacements” have pros and cons when considered in our terrestrial environment. What needs to be considered is that with a radically different environment, comes radically different reactions. Water and carbon might be the very last things capable of supporting life in some extreme planetary conditions.

Posted by Casey Kazan with Rebecca Sato.

This is the fourth and final post in a four-part series on Stephen Hawking's views on life in the universe.

Related Galaxy posts:

Stephen Hawking: Why Isn't the Milky Way "Crawling With Self-Designing Mechanical or Biological Life?"

Stephen Hawking: "Humans Have Entered a New Stage of Evolution"
Stephen Hawking: "Asteroid Impacts Biggest Threat to Intelligent Life in the Galaxy"

MIT Asks: How Would Extraterrestrial Astronomers Study Earth?
"The Great Silence" -A Galaxy Insight
Harvard-Smithsonian Scientists Zero In On Key Sign of Habitable Worlds

Sources:

http://www.rationalvedanta.net/node/131

http://www.physorg.com/news128057557.html

Comments

[Narendra Nath]

This write up in the name of Professor Hawking is an excellent one. Earth based life systems may not be found elsewhere in the Universe. It may well be based on Si, S or some other atomic species that can form long chain molecules in order to satisfy the logistics of life formation.It is right to assume that the atomic structure chemistry is the same throughout the universe. So it seems when we examine the Sun and other near celestial objects. But one may not be sure of far away objects. The conditions in the early universe were very different compared to the steady state affairs today or in our near past. It is quite possible that nanostructured atomic elements may be existing at some stage of evolution in a normal way. Their long chain molecular structure can show differnt traits for life bearing forms that we are unable to imagine easily today! Let our speculations cover an open mind on this aspect, instead of limiting ourselves to the science developed only during the past utmost 1000 years!

[SusanGrisantiGuitarist]

Beyond non-carbon-based life, what about other dimensional life? Certainly not impossible, they may be among us unperceived right now, & our detection equipment is still too primitive. As long as the Universe has been around, this might be the case.

[awake]

Nice So what about water? Isn’t at least water essential to life?