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What could alternate, alien forms of life look like?
All life as we know it relies on carbon and water. But researchers speculate this doesn't have to be the case.
- Life on Earth (and therefore all life we know) relies on carbon and water.
- Carbon and water make for excellent ingredients when making life, but many other elements could serve in their place under the right conditions.
- What are these alternative forms of life and under what conditions could they flourish?
All life on Earth, and thus, all life we've ever observed in the universe, shares a few basic characteristics. Its molecular structures are built using carbon, it relies on water to act as a solvent and facilitate chemical reactions, and it uses DNA or RNA as its blueprints.
These qualities seem so ubiquitous that most any compound we can find that contains carbon is called an organic compound. Carbon works very well as the basis for the chemistry of life. It can bond with many molecules, building structures large enough to be biologically relevant, and its bonds are strong and stable. Using water and DNA/RNA are also seemingly fine-tuned to enable life to exist.
But just because these properties of life are true on Earth doesn't mean they are true everywhere. In fact, we can readily imagine different environments where alternative forms of life can exist. Here are some of the major ways we think that life can vary from the standard we see on Earth.
An artists' rendering of organosilicon-based life. Organosilicon compounds contain carbon-silicon bonds.
Lei Chen and Yan Liang (BeautyOfScience.com) for Caltech
The same stuff that constitutes computer chips and electrical circuits may also constitute life somewhere in the universe. Carbon can form bonds with up to four other atoms at once, bind to oxygen, and form polymer chains, all of which make it ideal for the complex chemistry of life. Silicon, which lies just beneath carbon on the table of elements, also shares these characteristics.
Despite these qualities, silicon is still quite limited as a basis for life. It can only form stable bonds with a limited number of other elements; its polymers would be very monotonous, limiting its ability to form the complex compounds needed for life to occur; and silicon chemistry is not stable in aqueous, or watery, environments. Another issue is that when carbon oxidizes, it forms carbon dioxide, an easily expellable gas. When silicon oxidizes, it forms silicon dioxide, also known as silica, quartz, or sand. This solid waste would pose some serious mechanical challenges for any silicon-based life. Such a hypothetical lifeform would excrete bricks of sand every time it took a breath, which would make vacationing at the beach somewhat more horrifying.
Under certain conditions, silicon-based chemistry might be more favorable for life than carbon-based. Silicon chemistry would also be much more amenable to life in oceans of cold elements that we don't usually associate with life, such as liquid nitrogen, methane, ethane, neon, and argon. Places like these exist in the universe, notably in our own solar system: One of the major features of Saturn's largest moon, Titan, is its lakes of liquid ethane and methane.
An artist's depiction of a world with ammonia-based life. Ittiz [CC BY-SA 3.0]
Most of the chemical reactions that life relies on take place within a watery environment. Water dissolves many different molecules — it is a solvent, and having a good solvent is a prerequisite for the kind of chemistry that brings about life.
Like water, ammonia is also common throughout the galaxy. It's also capable of dissolving organic compounds like water, and, unlike water, it can also dissolve some metallic ones, opening up the possibility for some more interesting chemistry to be used in living things.
However, ammonia is also flammable in the presence of oxygen; has much lower surface tension than water, making it difficult to hold prebiotic molecules together for very long; and its melting and boiling points are much lower than water, at –78°C and –33.15°C, respectively. Thus, the chemistry of ammonia-based life would occur much more slowly, and commensurately, its metabolism and evolution would also be slower. An important caveat, though, is that these are the melting and boiling points that occur at Earth's atmospheric pressure. Under higher pressures, these values would rise.
One of the exciting features of ammonia-based life is that it could exist outside of the so-called habitability zone, or the range where liquid water can exist. Titan, for instance, may hold oceans of ammonia beneath its surface, and although it lies outside of our solar system's habitable zone, it could for this reason host life. Astrobiologists often point to Titan as a possible site of alternative life forms within our own solar system.
Just as a person can be left-handed or right-handed, so too can organic molecules. These molecules are mirror images of one another, but life, for whatever reason, wound up using one side or the other, which is called chirality. Amino acids, for instance, are "left-handed," while the sugars in RNA and DNA are "right-handed." For these molecules to interact with one another, they have to be of the correct kind of chirality; if protein chains are made with mixed-chirality amino acids, they simply don't work. But a protein chain constructed from right-handed amino acids, the opposite of what life on Earth uses, would work perfectly fine.
All of Earth's ecology depends on this convention. In order to eat, we need to consume food of the appropriate chirality. We can be infected and defend against infections of the appropriate chirality. Everything on Earth has the appropriate chirality, so this works just fine.
But alien life might evolve to use the opposite chirality as Earth. This life would be fundamentally quite similar to life on Earth — using carbon as its backbone and water as its solvent — but it would interact with us in one of two possible ways. First, it wouldn't be able to interact at all. Even if microbial life tried eat some other microbial life, the "reverse" sugars would be indigestible, and viruses wouldn't be able to bind to host cells. This would probably be a good thing, since we don't want to be infected with any alien diseases.
But there are critters on Earth that don't eat chiral nutrients, such as cyanobacteria. A comparable alien microbe would be able to eat as much as it wants, reproduce indefinitely, and would never be kept in check by predators since it itself would be of the wrong chirality. This would dramatically disrupt the food chain on an apocalyptic scale.
These alternative forms of life aren't the only ones that exist, but they're among the most likely. A lot of what we know about chemistry suggests that carbon- and water-based life will be the most common among the universe, but we've only ever had a sample of one to study: our own planet. If we find life on other worlds, we'll gain even greater insight into how living things come about.
- We are alone in the universe, says new Drake equation - Big Think ›
- Dark Forest theory: Why aliens haven't contacted us - Big Think ›
- The biology of aliens: How much do we know? - Big Think ›
So much for rest in peace.
- Australian scientists found that bodies kept moving for 17 months after being pronounced dead.
- Researchers used photography capture technology in 30-minute intervals every day to capture the movement.
- This study could help better identify time of death.
We're learning more new things about death everyday. Much has been said and theorized about the great divide between life and the Great Beyond. While everyone and every culture has their own philosophies and unique ideas on the subject, we're beginning to learn a lot of new scientific facts about the deceased corporeal form.
An Australian scientist has found that human bodies move for more than a year after being pronounced dead. These findings could have implications for fields as diverse as pathology to criminology.
Dead bodies keep moving
Researcher Alyson Wilson studied and photographed the movements of corpses over a 17 month timeframe. She recently told Agence France Presse about the shocking details of her discovery.
Reportedly, she and her team focused a camera for 17 months at the Australian Facility for Taphonomic Experimental Research (AFTER), taking images of a corpse every 30 minutes during the day. For the entire 17 month duration, the corpse continually moved.
"What we found was that the arms were significantly moving, so that arms that started off down beside the body ended up out to the side of the body," Wilson said.
The researchers mostly expected some kind of movement during the very early stages of decomposition, but Wilson further explained that their continual movement completely surprised the team:
"We think the movements relate to the process of decomposition, as the body mummifies and the ligaments dry out."
During one of the studies, arms that had been next to the body eventually ended up akimbo on their side.
The team's subject was one of the bodies stored at the "body farm," which sits on the outskirts of Sydney. (Wilson took a flight every month to check in on the cadaver.)Her findings were recently published in the journal, Forensic Science International: Synergy.
Implications of the study
The researchers believe that understanding these after death movements and decomposition rate could help better estimate the time of death. Police for example could benefit from this as they'd be able to give a timeframe to missing persons and link that up with an unidentified corpse. According to the team:
"Understanding decomposition rates for a human donor in the Australian environment is important for police, forensic anthropologists, and pathologists for the estimation of PMI to assist with the identification of unknown victims, as well as the investigation of criminal activity."
While scientists haven't found any evidence of necromancy. . . the discovery remains a curious new understanding about what happens with the body after we die.
The distances between the stars are so vast that they can make your brain melt. Take for example the Voyager 1 probe, which has been traveling at 35,000 miles per hour for more than 40 years and was the first human object to cross into interstellar space. That sounds wonderful except, at its current speed, it will still take another 40,000 years to cross the typical distance between stars.
Worse still, if you are thinking about interstellar travel, nature provides a hard limit on acceleration and speed. As Einstein showed, it's impossible to accelerate any massive object beyond the speed of light. Since the galaxy is more than 100,000 light-years across, if you are traveling at less than light speed, then most interstellar distances would take more than a human lifetime to cross. If the known laws of physics hold, then it seems a galaxy-spanning human civilization is impossible.
Unless of course you can build a warp drive.
Ah, the warp drive, that darling of science fiction plot devices. So, what about a warp drive? Is that even a really a thing?
Let's start with the "warping" part of a warp drive. Without doubt, Albert Einstein's theory of general relativity ("GR") represents space and time as a 4-dimensional "fabric" that can be stretched and bent and folded. Gravity waves, representing ripples in the fabric of spacetime, have now been directly observed. So, yes spacetime can be warped. The warping part of a warp drive usually means distorting the shape of spacetime so that two distant locations can be brought close together — and you somehow "jump" between them.
This was a basic idea in science fiction long before Star Trek popularized the name "warp drive." But until 1994, it had remained science fiction, meaning there was no science behind it. That year, Miguel Alcubierre wrote down a solution to the basic equations of GR that represented a region that compressed spacetime ahead of it and expanded spacetime behind to create a kind of traveling warp bubble. This was really good news for warp drive fans.
The problems with a warp drive
There were some problems though. Most important was that this "Alcubierre drive" required lots of "exotic matter" or "negative energy" to work. Unfortunately, there's no such thing. These are things theorists dreamed up to stick into the GR equations in order to do cool things like make stable open wormholes or functioning warp drives.
It's also noteworthy that researchers have raised other concerns about an Alcubierre drive — like how it would violate quantum mechanics or how when you arrived at your destination it would destroy everything in front of the ship in an apocalyptic flash of radiation.
Warp drives: A new hope
Credit: Primada / 420366373 via Adobe Stock
Recently, however, there seemed to be good news on the warp drive front with the publication this April of a new paper by Alexey Bobrick and Gianni Martre entitled "Introducing Physical Warp Drives." The good thing about the Bobrick and Martre paper was it was extremely clear about the meaning of a warp drive.
Understanding the equations of GR means understanding what's on either side of the equals sign. On one side, there is the shape of spacetime, and on the other, there is the configuration of matter-energy. The traditional route with these equations is to start with a configuration of matter-energy and see what shape of spacetime it produces. But you can also go the other way around and assume the shape of spacetime you want (like a warp bubble) and determine what kind of configuration of matter-energy you will need (even if that matter-energy is the dream stuff of negative energy).
Warp drives are simpler and much less mysterious objects than the broader literature has suggested.
What Bobrick and Martre did was step back and look at the problem more generally. They showed how all warp drives were composed of three regions: an interior spacetime called the passenger space; a shell of material, with either positive or negative energy, called the warping region; and an outside that, far enough away, looks like normal unwarped spacetime. In this way they could see exactly what was and was not possible for any kind of warp drive. (Watch this lovely explainer by Sabine Hossenfelder for more details). They even showed that you could use good old normal matter to create a warp drive that, while it moved slower than light speed, produced a passenger area where time flowed at a different rate than in the outside spacetime. So even though it was a sub-light speed device, it was still an actual warp drive that could use normal matter.
That was the good news.
The bad news was this clear vision also showed them a real problem with the "drive" part of the Alcubierre drive. First of all, it still needed negative energy to work, so that bummer remains. But worse, Bobrick and Martre reaffirmed a basic understanding of relativity and saw that there was no way to accelerate an Alcubierre drive past light speed. Sure, you could just assume that you started with something moving faster than light, and the Alcubierre drive with its negative energy shell would make sense. But crossing the speed of light barrier was still prohibited.
So, in the end, the Star Trek version of the warp drive is still not a thing. I know this may bum you out if you were hoping to build that version of the Enterprise sometime soon (as I was). But don't be too despondent. The Bobrick and Martre paper really did make headway. As the authors put it in the end:
"One of the main conclusions of our study is that warp drives are simpler and much less mysterious objects than the broader literature has suggested"
That really is progress.
The Black Death wasn't the only plague in the 1300s.
- In a unique study, researchers have determined how many people in medieval England had bunions
- A fashion trend towards pointed toe shoes made the affliction common.
- Even monks got in on the trend, much to their discomfort later in life.
Late Medieval England had its share of problems. The Wars of Roses raged, the Black Death killed off large parts of the population, and passing ruffians could say "Ni" at will to old ladies.
To make matters worse, a first of its kind study published in the International Journal of Paleopathology has demonstrated that much of the population suffered from another plague — a plague of bunions likely caused by a ridiculous medieval fashion trend.
If the shoe fits, it won't cause bunions
The outlines of a leather shoe from the King's Ditch, Cambridge. It is easy to see how these shoes might be constricting. Copyright Cambridge Archaeological Unit.
The bunion, known to medicine as "hallux valgus," is a deformity of the joint connecting the big toe to the rest of the foot. It is painful and can cause other issues including poor balance. The condition is associated with having worn constrictive shoes for a long period of time as well as genetic factors. Today, it is often caused by wearing high heeled shoes.
The medieval English didn't care for high heeled shoes as much as modern fashionistas, but there was a major fashion trend toward shoes with long, pointed toes called "poulaines" or "crakows" for their supposed place of origin, Krakow, Poland.
This trend, already silly-looking to a modern observer, got out of hand in a hurry. According to some records, the points on nobleman's shoes could be so long as to require tying them to the leg with string so the wearer could walk. At one point, King Edward IV had to ban commoners from wearing points longer than two inches. A couple years later, he saw fit to ban the shoes altogether.
But, just knowing that people back in the day made poor fashion choices doesn't prove they suffered for it. That is where digging up old skeletons to look at their feet comes in.
Beauty is pain: the price of high medieval fashion
To learn how bad the bunion epidemic was, the researchers looked to four burial sites in and around Cambridge. One was a rural cemetery where poor peasants were buried. Another was the All Saints by the Castle parish, which had a mixed collection of people that tended toward poverty. The Hospital of St. John's burial ground contained both the poor charges of a charity hospital and wealthy benefactors. Lastly, they considered the cemetery of a local Augustinian friary, home to monks and well-to-do philanthropists.
The team considered 177 adult skeletons that were at least a quarter complete and still had enough of their feet to make studying them possible. The remains were classified by age and sex by observation and DNA testing. Each was examined for evidence of bunions and signs of complications from the condition, such as falling.
Those buried in the monastery's graveyard were the most affected. Nearly half, 43 percent, of the remains found there had bunions. This includes five of the eleven members of the clergy they found. Twenty-three percent of those laid to rest at the Hospital of St. John had bunions, though only 10 percent of those at the All Saints by the Castle parish graveyard did.
The rural cemetery had a much lower rate of instances, only three percent, suggesting that these peasants were able to avoid at least one plague.
Overall, eighteen percent of the individuals examined had bunions, with men more likely to have them than women. Those at cemeteries known for exclusivity were more likely to have them as well, though it is clear that the condition also affected members of other classes. This makes sense, as it is known that these shoes had mass appeal.
The authors note that the rural cemetery having fewer cases is partly because that cemetery "went out of use prior to the wide adoption of pointed shoes, and it is likely that those residing in the parish predominately wore soft leather shoes, or possibly went barefoot."
Those skeletons with evidence of bunions were more likely to have fractures indicative of a fall. This was more common on those estimated or recorded as having lived past age 45.
In our much more enlightened times, 23 percent of the population currently endures having bunions, most of them women, and one of the leading culprits behind this is the high heeled shoe.
Some things never change.