SCIENCE6 - Reflections on the Search for Intelligent Extraterrestrial Life

My usual reason to write these blog articles is to learn something.  I love to research a subject, synthesize material from numerous sources, and produce a comprehensible story, particularly for complex subjects.  Well, I’ve really chosen a complex (and mind-boggling) subject this time, reflecting on the prospects of finding intelligent extraterrestrial life.  

I’ll start with a review of the history of UFOs, unidentified flying objects.  Perhaps we’ve already met up with intelligent aliens.  Then, I’ll step back and summarize what we know about the universe in terms of formation, evolution, and content, and try to put into perspective its vast scale in terms of time and distance, leading to the tantalizing prospects of other worlds like ours.  Then, I’ll cover our efforts to date in searching for intelligent extraterrestrial life, followed by what we’re doing in the near future.  Next, I’ll consider whether there are issues that may be show stoppers in our quest to locate and interact with advanced terrestrial life.  Finally, I’ll conclude with some speculative ideas about future space travel, the kind of intelligent life Earthlings might find some day, and some questions about the universe.

My principal sources include “The History of UFO’s,” history.com; “Is there life on other planets?”, exoplanets.nasa.gov; “Intelligent life probably exists on distant planets even if we can’t make contact, astrophysicist says,” washingtonpost.com; “Warp drives:  Physicists give chance of faster-than-light space travel a boost,” eathsky.org; “What could alternate, alien forms of life look like?”, bigthink.com; “Frequently asked questions in cosmology,” astro.ucla.edu, and “Interstellar travel,” Wikipedia.

Have we already experienced extraterrestrial intelligent life, aka alien UFO contacts?

The following is adapted from “History of UFO’s,” history.com.

UFO sightings have been reported throughout recorded history and in various parts of the world, raising questions about life on other planets and whether extraterrestrials have visited Earth.  UFO sightings became a major subject of interest - and the inspiration behind numerous films and books - following the development of rocketry after World War I.

The first well-known UFO sighting occurred in 1947, when a businessman pilot claimed to see a group of nine high-speed objects near Mount Rainier in Washington while flying his small plane.  He said they moved “like saucers skipping on water.”  In the newspaper report that followed, it was mistakenly stated that the objects were saucer-shaped, hence the term “flying saucer.”

Also in 1947, a rancher came across a mysterious 200-yard-long wreckage near an Army airfield in Roswell, New Mexico.  Local papers reported it was the remains of a flying saucer.  The U.S. military issued a statement saying that it was just a weather balloon, though the newspaper photograph suggested otherwise.  To some, this seemed like a government cover-up.  Fifty years later, the military issued a subsequent statement admitting that the Roswell wreckage was part of a top-secret atomic espionage project.

 

The 1947 Roswell incident was perhaps the most famous of UFO sightings.

Sightings of unidentified aerial phenomena increased, and in 1948, the U.S. Air Force began an investigation of these reports.  Cold War tension was mounting, and the initial opinion was that the UFOs were most likely sophisticated Soviet aircraft, although some researchers suggested that they might be spacecraft from other worlds.

In 1952, the longest-lived of the official inquiries into UFOs, Project Blue Book, was commissioned, headquartered at Wright-Patterson Air Force Base in Dayton, Ohio.  From 1952 to 1969, Project Blue Book compiled reports of more than 12,000 sightings or events, each of which was ultimately classified as (1) “identified” with a known astronomical, atmospheric, or artificial (human-caused) phenomenon or (2) “unidentified.”  The latter category, approximately 6 percent of the total, included cases for which there was insufficient information to make an identification with a known phenomenon.

The American obsession with the UFO phenomenon led the Central Intelligence Agency in 1952 to prompt the U.S. government to establish an expert panel of scientists, headed by H.P. Robertson, a physicist at the California Institute of Technology, to investigate the phenomena.  The Robertson Panel conclusions were that (1) 90 percent of the sightings could be easily attributed to astronomical and meteorological phenomena (e.g., bright planets and stars, meteors, auroras, ion clouds) or to such earthly objects as aircraft, balloons, birds and searchlights; (2) there was no obvious security threat; and (3) there was no evidence to support the extraterrestrial spacecraft theory.  Parts of the panel’s report were kept classified until 1979, and this long period of secrecy helped fuel suspicions of a government cover-up.

A second committee was set up in 1966 at the request of the Air Force to review the most interesting material gathered by Project Blue Book.  Two years later this committee, which made a detailed study of 59 UFO sightings, released its results as “Scientific Study of Unidentified Flying Objects” - also known as the Condon Report, named for Edward U. Condon, the physicist who headed the investigation.  Like the Robertson Panel, the committee concluded that there was no evidence of anything other than commonplace phenomena in the reports and that UFOs did not warrant further investigation.  This, together with a decline in sighting activity, led to the dismantling of Project Blue Book in 1969.

In the 1950s and 60s, multiple UFO sightings were reported around Area 51 in Nevada, a site used variously by the CIA, U.S. Air Force, and Lockheed Martin to test flights of experimental aircraft, or “black aircraft.”  These mysterious planes helped fuel rumors that Area 51 was used to conduct experiments on extraterrestrial life and their spacecraft.

The bottom line here is that optical illusions and the psychological desire to interpret images are known to account for many visual UFO reports, and at least some sightings are known to be hoaxes.  Radar sightings, while in certain respects more reliable, fail to discriminate between artificial objects and meteor trails, ionized gas, rain, or thermal discontinuities in the atmosphere.  “Contact events,” such as abductions, are often associated with UFOs because they are ascribed to extraterrestrial visitors.  However, the credibility of the abductions is disputed by most psychologists who have investigated this phenomenon.

The consensus of scientists is that we have not yet had contact with intelligent extraterrestrials.

What We Know about the Universe

Much of the following was adapted from “What is the Universe?” and “What is an Exoplanet?” at exoplanets.nasa.gov.

The universe is everything.  It includes all of space, and all the matter and energy that space contains.

Prevailing theories say that our universe was created from a single point with infinite density by the “Big Bang” explosion, roughly 13.8 billion years ago.  After an initial expansion, the universe cooled sufficiently to allow the formation of subatomic particles, and later simple atoms.  Giant clouds of these earliest elements later coalesced through gravity to form galaxies, stars, planets, moons, asteroids, and comets.  Earth formed about 4.54 billion years ago by accumulation from a cloud of dust and gas left over from the formation of the Sun.

Galaxies are gravity-bound systems of stars; our Sun is a star in the Milky Way galaxy.

For nearly two-thirds of the time since the universe began, Earth did not even exist.  Single-celled life on Earth began about 3.8 billion years ago, and the first of our species (homo sapiens) appeared only about 195,000 years ago.  In other words, the universe has existed over 70,000 times longer than our species has.  By that measure, almost everything that’s ever happened did so before humans existed.  In a cosmic sense, we just got here.

A couple of mind-numbing stats:  The universe is about 93 billion light years in diameter.  (A light year is the distance that light travels in one Earth year at a speed 186,000 miles per second:  5.88 trillion miles.)  Our home Milky Way galaxy is about 105,000 light years in diameter. 

An artist’s conception of the spiral Milky Way galaxy is shown below.  The Sun is located about 26,000 light-years away from the center of the galaxy.

 

Artists conception of the Milky Way galaxy with the Sun's location annotated.  The galaxy's center is the bright white spot, where hot massive stars crown together.

For additional perspective:  The Earth orbits the Sun at an average distance of about 93 million miles; that’s 0.0000158 lightyear.  It takes sunlight 8.33 minutes to reach Earth.

According to NASA (National Air and Space Administration), the Milky Way galaxy, contains at least 100 billion stars, and the observable universe contains at least 100 billion galaxies - all thought to have supermassive black holes at their centers.  (A black hole is a region of space having a gravitational field so intense that no matter or radiation can escape.  In 2019, we succeeded in producing the first image of a black hole.)

If galaxies were all the same size, that would give us 10 thousand billion billion (or 10 sextillion) stars in the observable universe - and we think that most of those stars have their own planets, known as exoplanets.

The universe also seems to contain a bunch of matter and energy that we can’t see or directly observe.  All the stars, planets, moons, asteroids, comets, black holes, etc. together, represent less than 5% of the stuff in the universe.  About 27% of the remainder is dark matter, and 68% is dark energy, neither of which are even remotely understood today.  Dark matter and dark energy are labeled “dark” because scientists can’t seem to directly observe them.  Also, the universe is continuing to expand, and at a rate that is actually speeding up; scientists don’t know why yet.

Efforts to-Date to Find Intelligent Extraterrestrial Life

For millennia, humans have gazed in wonder at the stars, trying to understand their nature and import.  (With human eyesight, 5 to 10 thousand stars and eight galaxies are visible from Earth.)  Our search for intelligent extraterrestrial life is revealing important details about our own place in the universe - where we came from, how life came about and, perhaps, where we’re headed.

Monitoring, Solar System Exploration, Interstellar Probes, Space Telescopes.  We started our systematic search shortly after the advent of radio in the in the early 1900s by monitoring electromagnetic radiation for signs of transmissions from civilizations on other planets.  Focused international efforts in SETI (Search for Extraterrestrial Intelligence) programs have been going on since the 1980s.  We have also sent signals into space in the hope that they will be picked up by an alien intelligence.  There have been no positive results so far, but SETI efforts continue today.

In the span of a single human lifetime, we have visited the Moon; space probes have voyaged to the outer solar system and sent back the first up-close images of the four giant outermost planets and their countless moons; rovers wheeled along the surface on Mars; and humans constructed a permanently-crewed, Earth-orbiting space station.  It appears that there is no other intelligent life in our solar system.

In the 1970s, we launched four interstellar probes to explore the environment of our Milky Way galaxy:  Pioneer 10 (1972), Pioneer 11 (1973), Voyager 1 (1977), and Voyager 2 (1977).  In case these probes were “discovered” by intelligent aliens, the Pioneer spacecraft carried pictorial messages and the Voyager spacecraft carried audio recordings and encoded pictures.  The Pioneer probes stopped transmitting data in 2003 and 1995, respectively, while the Voyager probes are still functional.  In 2006, we launched the New Horizons interstellar probe which continues to transmit environmental data.  Many other interstellar probes have been proposed, but have not yet become actual programs.

We developed telescopes only a few hundred years ago, and since then the dimensions of our observable universe have expanded exponentially with technological advances and the insights of general relativity and quantum physics.  

There are several methods in use today to find exoplanets by analyzing observation data from ground and space telescopes.  Orbiting planets cause stars to wobble in space, changing their position in relation to nearby stars, and changing the color of the light that astronomers observe.  When a planet passes directly between its star and an observer, it dims the star’s light by a measurable amount.  Astronomers can take picture of exoplanets by removing the overwhelming glare of the stars they orbit.  An finally, light from a distant star is bent and focused by gravity as a planet passes between the star and Earth. 

One of the best tools scientists have to begin narrowing the search for exoplanets, and specifically worlds that could support life, is a concept known as the “habitable zone.”  It’s the orbital distance from a star where temperatures would potentially allow liquid water to form on a planet’s surface.  This distance varies, depending on the size and temperature of exoplanet’s star.  Many other conditions also would be required:  a planet of suitable size with a suitable atmosphere, and a stable star, not prone to erupting in sterilizing flares.  The habitable zone is really just a way to make the first cut, and zero in on the planets with the best chance of possessing habitable conditions.

 

Habitable zones for exoplanets, shown here in green, depend on how hot their stars are.

 

Early Space Telescope Programs.  To avoid having to look through Earth’s obscuring atmosphere from the ground, we launched the first large space telescopes that delivered jaw-dropping views of more distant parts of the cosmos than ever before.  NASA’s Hubble (1990) and Spitzer (2003) space telescopes opened a window on the atmospheres of these far distant worlds, capturing early evidence of the gases present.  That put us on the verge seeing more detail than ever before, scanning the gases of these worlds for possible signs of life. 

NASA operates a program to accomplish this:  NASA's Science, Technology and Mission Management Office for the Exploration of Exoplanets.  The program's primary goals, as described in the 2014 NASA Science Plan, are to discover planets around other stars, to characterize their properties, and to identify planets that could harbor life.

NASA’s array of technological marvels to do this include the Kepler Space Telescope (2009), now retired, and its successor, TESS, the Transiting Exoplanet Survey Satellite (2018), still operating on an extended mission.  Both were built specifically to hunt for exoplanets, using large telescopes outfitted with advanced spectroscopy instruments.

Exoplanets.  In 1995, analyzing data from a ground-based observatory, scientists discovered the first exoplanet, a gas giant like Jupiter, with a mass about 150 times that of Earth, orbiting a star 50 light-years distant from Earth.

So far, using the techniques outlined above, there have been almost 5,000 confirmed discoveries of exoplanets in our galaxy - about a fifth of them in Earth’s size-range - and the number of confirmed exoplanets is rapidly expanding.

Exoplanets come in a wide variety of sizes, from gas giants larger than Jupiter, to small, rocky planets about as big around as Earth or Mars.  They can be hot enough to boil metal or locked in deep freeze. They can orbit their stars so tightly that a “year” lasts only a few days; and they can orbit two suns at once.  Some exoplanets are starless rogues, wandering through the galaxy in permanent darkness.

 

Exoplanets come in a wide variety of types.

There are 81 visible stars within 40 lightyears of Earth.  Among these stars, there are up to (confirmed and unconfirmed) 15 exoplanets located in the habitable zone of their stars.  Proxima Centauri is the closest star to Earth (after the Sun) at a distance of 4.25 lightyears.  On August 24, 2016, the discovery of an Earth-size exoplanet (Proxima Centauri b), orbiting in the habitable zone of Proxima Centauri, was announced.

We have yet to find another “Earth” with life, intelligent or not.  No convincing evidence of advanced technology - artificial signals by radio or other means, or the telltale sign of, say, massive extraterrestrial engineering projects - has yet crossed our formidable arrays of telescopes in space or on the ground.

The good news is that since it is estimated that there is a least one planet for every star in our galaxy (meaning that there’s something on the order of billions of planets in our galaxy alone), the odds of finding hospitable worlds that would support intelligent life are high.

What We’re Doing Next

In the years and decades ahead, NASA, as well as academic and international partners, will design and build the next generation of instruments to sift through light from other worlds, and other suns.  The goal: unambiguous evidence of other living, breathing worlds. 

Analyzing Exoplanet Atmospheres.  Exoplanets’ own skies could hold signs of potential life - to be revealed in the future by detailed analysis of the atmospheres of planets well beyond our solar system.  The focus will be on the six main elements associated with life on Earth: carbon, nitrogen, oxygen, phosphorous, sulfur, and hydrogen.

When we analyze starlight passing through the atmosphere of a distant planet, with a technique known as transmission spectroscopy, the effect will look like a barcode.  The slices missing from the light spectrum can tell us which ingredients are present in the alien atmosphere.  One pattern of black gaps might indicate methane, another, oxygen.  Seeing those together could be a strong argument for the presence of life.  Or we might read a barcode that shows the burning of hydrocarbons; in other words, smog.

Analyzing exoplanet atmospheres will produce bar codes to identify chemicals associated with the potential of life.

 

Advanced Space Telescopes.  This next generation of space telescopes will bring a sea change in the planet search:  measuring the atmospheres of the planets themselves.  A pressing goal is characterizing exoplanets - getting to know their intrinsic attributes to assess the possibility of habitability.

First on deck for this new generation:  NASA’s James Webb Space Telescope, a giant among robotic spacecraft, launched on December 25, 2021, that looks like nothing previously seen.  Imagine a huge, segmented, gold-coated light-collecting dish attached to a giant silver sunshade - a little like a piece of honeycomb riding atop a shingle that would cover the better part of a tennis court.

 

Concept drawing of the James Webb Space Telescope.

The Webb telescope will plumb the depths of the universe and try to uncover secrets of the earliest galaxies, black holes, and other cosmological phenomena.

Recall that the universe came into existence 13.8 billion years ago.  Referring to the figure below:  A historic progression of space telescope capability is shown in terms of how far the telescopes can look into space, which equates to how far they can look back in time.  (Because light takes time to travel from one place to another, we see objects not as they are now but as they were at the time when they released the light that has traveled across the universe to us.  Astronomers can therefore look farther back through time by studying progressively more-distant objects.)

Ground based observations can see what the universe looked like about 6 billion years after creation (or 13.8 - 6 = 7.8 billion years ago).  Improvements in Hubble Telescope technology allowed us to see the universe as it was from 4 billion to 480 million years after the Big Bang.  The James Webb Space Telescope will allow us to see the early universe as it was only 250 to 100 million years after the Big Bang, when the first stars and galaxies started to form.

 

The James Web Space Telescope will show us what the early universe was like only 250-100 million years after its birth.  The redshift numbers at the bottom of the chart represent the increase in wavelength of light as the distance from Earth increases.

Another of the Webb Telescope’s jobs will be to capture starlight shining through the atmospheres of exoplanets.  In a sense, Webb will take “samples” of exoplanet atmospheres.  In some cases, this might include searching for potential signs of life in these gases - biosignatures - although that investigation is far more likely to be taken up by even more powerful space telescopes in the future.

The next telescope that will advance the goal of exoplanet characterization, likely to launch in the mid-2020s, the Roman telescope, will include an intricate piece of technology called a coronagraph.  This system of masks, shape-changing mirrors, and detectors inside the telescope will blot out the light from a star, revealing the planets around it.  The pixels of light from the planets themselves can be split into a spectrum, allowing spectroscopic analysis.

The Roman telescope will have the power to capture direct images of large, gaseous planets unlikely to be habitable worlds, though probably not smaller targets.  But this technology demonstration will point the way to the future:  spaceborne instruments that could look in on a rocky planet the size of Earth and search for familiar gases - oxygen, methane, carbon dioxide - that, seen together, might indicate the presence of life.

Future telescopes might even pick up signs of photosynthesis - the transformation of light into chemical energy by plants - or even gases or molecules suggesting the presence of animal life.  Intelligent, technological life might create atmospheric pollution, as it does on our planet, also detectable from afar.

As we search the heavens for a possible twin to Earth, we’ll have to take into account the stages of a planet’s growth - infancy to maturity.  Earth hasn’t always looked like the blue orb we know so well.  Earth has been:  a lava-covered rock with a poisonous atmosphere, an ocean world with the bare beginnings of microbial life, a steaming tropical riot of earth-shaking dinosaurs, and an Ice Age expanse where cave-dwelling humans hunted mammoths.  It’s only in the last few thousand years that anyone would say that there was intelligent life on Earth.  Timing is everything.

Show Stoppers

Let’s review what we think we know about the prospects of finding intelligent extraterrestrial life.  Based on our astronomical observations so far, there should be almost countless exoplanets in the universe.  It seems reasonable to assume (high statistical likelihood) that there are other worlds out there with conditions to support life as we know it, and that some of those worlds have matured enough to have intelligent life.  After a slow start with ground-based observations, we are now using powerful space telescopes to hunt for such worlds.  We can expect that the number of confirmed exoplanets will grow quickly from nearly 5,000 today to much larger numbers in the near future.  And we now have the capability, with future improvements coming soon, to start analyzing the atmospheres of exoplanets to identify the elements of life, including advanced technological life.  It may take decades, but many scientists are confident that we will be able to find intelligent life elsewhere in the universe.

But the big question is:  Will we ever be able to conveniently communicate or interact with intelligent beings on other worlds?  The answer to that question, based on our current understanding of the universe and its physical laws, is:  Probably not.  The reasons are the vast distances, and travel or signal transmission times involved.  There may be over 10 sextillion exoplanets in the universe, but the thought of traveling the universe is truly mind boggling.

Away from our solar system, the closest star to Earth, Proxima Centauri, 4.25 light years away, or about 25 trillion miles.  If the interstellar Voyager 1 spacecraft were to travel (at its max speed of 38,210 mph) to Proxima Centauri, it would take over 75,000 years to finally arrive. (And if someone on Earth were communicating with intelligent life in the Proxima Centauri system, it would take 4.25 Earth years, via radio waves traveling at the speed of light, for a message to get there; a response would take another 4.25 years to reach Earth).

Thus, the speeds required for practical interstellar travel in a human lifetime far exceed what current methods of space travel can provide.  Many different spacecraft propulsion systems have been proposed to give spacecraft much higher speeds, including nuclear propulsion, beam-powered propulsion, and methods based on speculative physics.  Another higher-speed issue is the danger from collisions by the spacecraft with cosmic dust and gas.

Alternate strategies have been proposed to deal with these problems, ranging from enroute suspended animation of the crew, to giant arks that would carry entire societies and ecosystems, to microscopic space probes.

For both crewed and uncrewed interstellar travel, considerable technological and economic challenges need to be met.  Even the most optimistic views about interstellar travel see it as only being potentially feasible decades from now.

Even if we could travel at the speed of light, the distances and time requirements seem insurmountable.

 

Einstein's General Theory of Relativity says we cannot exceed the speed of light:  186,000 miles (or 300,000,000 meters) per second.

There’s a high statistical likelihood of intelligent life-forms having evolved elsewhere in the universe, but a very low probability that we’ll be able to communicate or interact with them.  If humanity ever wants to travel easily between stars, people will need to go faster than light.  But so far, faster-than-light travel is possible only in science fiction.

Final Reflections

Here are a few final thoughts on potential faster-than-light space propulsion, alternative alien life forms, and questions about the universe.  There is so much that we don’t know yet!

Warp Drives.  The following is adapted from “Warp drives:  Physicists give chance of faster-than-light space travel a boost,” eathsky.org.

There have been many fictional references to faster-than-light speed space travel.  In Isaac Asimov’s science fictional Foundation series of books, humanity can travel from planet to planet, star to star, or across the universe almost instantaneously, using jump drives that access a higher dimension Asimov called hyper-space.  The astronauts in the movies “Interstellar” and “Thor” - use wormholes to travel between solar systems in seconds.  (Wormholes are tunnels through space-time that connects two distant points in space.)  Another approach - familiar to “Star Trek” fans - is warp drive technology, that exploits the curved fabric of space.  Warp drives are theoretically possible, if still far-fetched technology. 

 

Artist's concept of faster-than-light travel through a wormhole.

Physicists’ current understanding of time in space comes from Albert Einstein’s theory of General Relativity.  General Relativity states that space and time are fused in a four-dimensional continuum, “the curvature of space and time,” and that nothing can travel faster than the speed of light.  General Relativity also describes how mass and energy warp spacetime - hefty objects like stars and black holes curve spacetime around them.  This curvature is what you feel as gravity.  Early science fiction writers John Campbell and Asimov saw this warping as a way to skirt the speed limit.

Two scientific papers in March 2021 - one by Alexey Bobrick and Gianni Martire, and another by Erik Lentz - provide solutions that seem to bring warp drives closer to reality.  (Read the above reference for a fuller explanation.)  It is essential to point out that these exciting developments are preliminary mathematical models only, and need much more development.  And of course, we’d need experimental proof.  Yet, the science of warp drives is coming into view.

In the words of Captain Picard: “Things are only impossible until they are not.”

Alternate Alien Life Forms.  The following is adapted from “What could alternate, alien forms of life look like?”, bigthink.com.

All life on Earth 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.  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 that life may vary from the standard we see on Earth.

 

Alien biochemistry may be entirely different from human biochemistry as shown above.

Silicon.  Silicon, 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; and silicon chemistry is not stable in water.  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.

Silicon chemistry would be 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.

Ammonia.  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; can’t hold pre-life molecules together for very long; and its melting and boiling points are much lower than water, at -108.4 degrees F and -27.67 degrees F, respectively.  The chemistry of ammonia-based life would occur much more slowly; its metabolism and evolution would also be slower.

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.

Alternate Chirality.  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 on Earth, 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.

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.

Universal Questions.  The following is adapted from “Frequently asked questions in Cosmology,” astro.ucla.edu.

The current best fit model for the creation of the universe is the Big Bang theory - the idea that the universe began about 13.8 billion years ago as just a single point, then expanded and stretched to grow as large as it is right now - and it is still stretching, at an accelerating rate.  The evidence for the Big Bang comes from many pieces of observational data that are consistent with the Big Bang.  But, it’s important to realize that none of these prove the Big Bang, since scientific theories are not yet proven.

There are many unresolved issues or questions yet to be resolved concerning the creation and nature of the universe, including:  Is the Big Bang the correct creation model?  What came before the Big Bang?  What is the shape of the universe:  round, flat, or other?  Why is the universe still expanding and at an accelerating rate?  Is the universe infinite?  Will the universe expand forever or collapse?  How/when will the universe end?  Are there other (parallel) universes?  What are black holes?  What are dark matter and dark energy, and how do they affect the universe? 

 

Artist's conception of multiple, parallel universes.

 

All of which goes to say, most of the universe that can be known, remains unknown.