The universe (as we know it)

Finally, the long-promised, long-delayed blog on all things cosmic.

As you might remember, I recently attended a weeklong course on the origins of the universe … well, to be more precise, the origins and current nature of the universe as we feeble human beings understand it. For those of you who have absolutely no interest in the origins of the universe, I’ll be back soon with other less … um … lofty topics. Meanwhile, here’s a picture of the Andromeda galaxy—the one closest to our own Milky Way—to tempt you to read on.

Rather than trying to tell you everything I brought away from my week, I’ll share a few particularly fascinating tidbits in hopes you’ll find them fun, too: Where did it all come from? Is there life elsewhere in our universe? Is there more than one universe?

How big is the universe and where did it all came from?

You’ve likely all heard of the “big bang.” The point about 14 billion years ago when the whole universe (as we know it) was created, when an unimaginably dense concentration of space/time/matter expanded with such suddenness that all of existence as we know it was created in an instant. Within seconds, time and space had expanded astronomically, spreading out enough that light could penetrate the mass, and the atoms that would become stars and galaxies began to coalesce. The atoms formed stars, the stars collected into galaxies, and the galaxies into galaxy clusters. Over a few million years, an eye blink in cosmic time, the structure of the universe as we know it had begun to emerge.

We now have the technology to see beyond our own galaxy and far, far into the distance (which is also into the distant past—nearly back to the big bang). What we see is billions upon billions of galaxies in various stages of evolution. For an idea of how many we’re talking about, try this. Hold up a quarter at arm’s length. Now, imagine a part of the sky the size of George Washington’s eye on that quarter. The Hubble space telescope stared a spot of sky that size—one eye’s worth—a part of the sky where regular telescopes saw no stars at all, and this is what Hubble saw. This is the Hubble eXtreme Deep Field or XDF. 

Here's the amazing part: each of those blurry spots and each of those pinpoints of light, even the tiniest and most faint, is a galaxy—not a star, but a galaxy containing many billions of stars, like the Andromeda galaxy shown above. Multiply the number of galaxies in this picture by the number of George Washington’s eyes it would take to cover the whole sky, multiply that by 2 to account for the southern hemisphere, and you have an idea of how many galaxies there are in the currently known universe. This picture looks back more than 10 billion light-years.

So, given those billions of galaxies, each of which has billions of stars, how likely is it that there is a star/sun somewhere with a plant that is home to life as we know it?

Is there life elsewhere in the universe?

The question of whether there is (or ever has been) life on other planets is much more complicated than it might seem at first. First, there’s the question of what me mean by “life.” Usually we mean intelligent life—someone we could communicate with, for better or worse. But bacteria and amoebas are also life. Then there’s the question of time frame. Do we mean is there life now, or has there ever been (will there ever be) life? And then we have to consider what stage of evolution we mean. Humans have taken about 7 million years to evolve to our present state … what are the odds that we’ll find intelligent life that is currently at precisely the stage of its evolution where it is able (and wants) to communicate?

Which raises the problem of distance. A signal travelling at the speed of light from (or to) the nearest known planet that might host life would take about 2,700 years to reach us (or vice versa). That’s a long wait for a reply. Actual space travel seems unimaginable. The fastest outward-bound spacecraft yet, Voyager I, has covered 1/600th of a light-year in 30 years. That means it would take a spaceship almost 50 million years to get to the closest known planet that might be able to harbor life. I’m guessing it would be hard to find volunteers for the trip.

Still, despite all this, folks are looking for other life in the universe. In our own solar system, they’re looking for signs of past or present life on Mars and on the moons of Jupiter and Saturn. This search won’t yield “intelligent” (i.e., human-like) life, but it could tell us some interesting stuff about the history of our own solar system.

And then there’s the search for life on planets circling other stars, i.e., extrasolar planets or exoplanets. The first sighting of such a planet happened in 1988. Now, nearly 900 exoplanets have been confirmed, and almost 3500 other observations have been identified as likely exoplanets. (For a running count, click here.). Still, virtually all of these would be uninhabitable—too gassy, too hot, too cold, too massive.

The hunt for a planet that could sustain life—one of reasonable size located in a star’s so-called “habitable zone” (also called the “Goldilocks zone”)—continues. Over 250 “candidate” planets in the habitable zone have already been identified in the relatively few solar systems that have been studied to date. Considering that there are estimated to be about 100 billion planets in our Milky Way alone (one of billions of galaxies in the universe), it seems very likely that life exists somewhere out there.

An important question (even for non-astronomy buffs) was raised during the Q & A after a talk at my course. The questioner asked whether we should be “excited or afraid” at the prospect of contact with other life. The speaker, an astrophysicist who hunts for Earth-like planets as her day job, answered, “Maybe they should be afraid.” After the chuckles died, she said, more seriously, “We’d better get our house in order, because we’re going to have company.”

Hearing the question, I was first struck by the sort of xenophobic assumption it conveyed. Why would we assume that another civilization would be frightening instead of friendly, enlightening, helpful, wise? Also, why would we assume that another civilization, should such a thing exist, would be interested in contacting us? If they’re advanced enough to get here, they’d likely know a lot about us before they arrived. You have to wonder how eager they’d be to visit a world where the supposedly "intelligent" residents kill each other and destroy their own home planet. Indeed, maybe they should be afraid!

Are there multiple universes?

Physicists are on the hunt for a unifying theory that would join currently incompatible models of how the cosmos works—a so-called “theory of everything.” That search has led to complicated new theories (about strings, ‘branes, etc.), which have led, in turn, to suggestions that ours may not be the only universe.

Over the years, I’ve heard several arguments for the possibility that more than one universe exists. On one level, this seems nonsensical—how could there be something else outside of everything that is? Don't worry if you find it baffling. Famous physicists have publicly agreed that the notion is incomprehensible, if mathematically logical. Our brains, my astrophysicist teacher said, just don’t seem to be the right tools for understanding this notion. But “the math,” as physicists like to say, “is clear”: multiple universes are definitely possible.

During my week-long course, I heard a talk by Brian Greene, author of (among other things) The Hidden Reality: Parallel Universes and  the Laws of the Deep Cosmos. Greene’s candidate for a unifying theory is string theory. Whole books have been written about this, and although I learned a ton from his talk, I remain deeply confused and won’t even pretend to explain it here.

But this much I got: For string theory to work, a few things must be true. Most importantly, there have to be 11 dimensions (plus time) instead of the three dimensions we’re used to. These additional dimensions are not visible to us because they are so tiny. Greene uses the analogy of a wire that, at a distance, looks like it has just one dimension–length. But to an ant crawling around its circumference, it has three. The extra 10 dimensions, he says, are rolled up inside the ones we know, much as the ant’s path is rolled up in what we see as the “length” of the wire. These various dimensions exist as strings, and these strings vibrate at different frequencies. In fact, what we understand to be different particles (electrons, neutrons, quarks, etc.) are just strings vibrating at different frequencies.

And what, you may ask, does this have to do with multiple universes? Couldn’t those little ant spaces just exist here? Well, not exactly. If other dimensions are curled up as invisible strings, these strings could have an infinite number of potential shapes, each of which would have a different vibrational frequency. This infinite variety of vibrational frequencies would point to an infinite number of possible particles and an infinite number of possible laws to govern them.

So what? Well, Greene asks, why are we only aware of three dimensions if there are so many? Why only a finite number of elements and a finite number of laws to explain them? His answer: because this particular universe, with this particular set of laws is the one that allows us to exist. All the other possible types of existence—the other possible dimensions, frequencies, and laws—exist because there are other universes where those particular forms of reality operate.

Again, making sense of this may simply be beyond the ability of the typical human brain. Although Greene and his colleagues seem to get it, I, for one, am left scratching my head. So rather than belabor it further, I’ll just leave it to you to imagine how exciting it was to hear this from someone who explained it really well (with great visuals). And who sent the audience away not stuck in confusion about the science but instead wondering at the anthropocentrism that allows us to think that our universe is the only universe. Why would that be the case?!

Which takes me back to an earlier blog about reflections on being and nothingness, also evoked by this course. I refer you to that discussion for further mind-numbing exploration of who we are in the cosmos.

And with that, I’ll wrap up the topic of astrophysics with a grateful nod to the joy and privilege of retirement. It was such fun to be able to dedicate a week to the sheer joy of learning more about a life-long avocation. And as a bonus, I figure it may have helped to keep my brain lubricated.