Posted Thursday, March 21, 2013, at 2:46 PM
The Universe is a wee bit older than we thought. Not only that, but turns out the ingredients are a little bit different, too. And not only that, but the way they’re mixed isn’t quite what we expected, either. And not only that, but there are hints and whispers of something much grander going on as well.
So what’s going on?
The European Space Agency’s Planck mission is what’s going on. Planck has been scanning the entire sky, over and over, peering at the radio and microwaves pouring out of the Universe. Some of this light comes from stars, some from cold clumps of dust, some from exploding stars and galaxies. But a portion of it comes from farther away…much farther away. Billions of light years, in fact, all the way from the edge of the observable Universe.
This light was first emitted when the Universe was very young, about 380,000 years old. It was blindingly bright, but in its eons-long travel to us has dimmed and reddened. Fighting the expansion of the Universe itself, the light has had its wavelength stretched out until it gets to us in the form of microwaves. Planck gathered that light for over 15 months, using instruments far more sensitive than ever before.
The light from the early Universe shows it’s not smooth. If you crank the contrast way up you see slightly brighter and slightly dimmer spots. These correspond to changes in temperature of the Universe on a scale of 1 part in 100,000. That’s incredibly small, but has profound implications. We think those fluctuations were imprinted on the Universe when it was only a trillionth of a trillionth of a second old, and they grew with the Universe as it expanded. They were also the seeds of the galaxies and the clusters and galaxies we see today.
What started out as quantum fluctuations when the Universe was smaller than a proton have now grown to be the largest structures in the cosmos, hundreds of millions of light years across. Let that settle in your brain a moment.
And those fluctuations are the key to Planck’s observations. By looking at those small changes in light we can find out a lot about the Universe. Scientists spent years looking at the Planck data, analyzing it. And what they found is pretty amazing:
- The Universe is 13.82 billion years old.
- The Universe is expanding a bit slower than we expected.
- The Universe is 4.9 percent normal matter, 26.8 percent dark matter, and 68.3 percent dark energy.
- The Universe is lopsided. Just a bit, just a hint, but that has profound implications.
What does all this mean? Let’s take a quick look, one at a time, at these results.
The Universe is 13.82 billion years old.
The age of the Universe is a little bit higher than we expected. A few years ago, the WMAP spacecraft looked at the Universe much as Planck has, and for the time got the best determination of the cosmic age: 13.73 +/- 0.12 billion years old.
Planck has found that the Universe is nearly 100 million years older than that: 13.82 billion years.
At first glance you might think this is a really different number. But look again. The uncertainty in the WMAP age is 120 million years. That means the best estimate is 13.73 billion years, but it could easily be 13.85 or 13.61. Anything in that range is essentially indistinguishable in the WMAP data, and 13.73 is just in the middle of that range.
And that range includes 13.82 billion years. It’s at the high end, but that’s not a big deal. It’s completely consistent with the older estimate, but Planck’s measurements are considered to be more accurate. It will become the new benchmark for astronomers.
The Universe is expanding a bit slower than we expected.
The Universe is expanding, and has been ever since the moment it was born. We can measure the speed of this expansion in various ways; for example, looking at distant exploding stars. We can measure how fast they are moving away from us, swept along with the expansion of space, by seeing how much their light is redshifted (I have details about how this works in an earlier post on redshifts and the expansion of the Universe). We can measure their distance, too, using various methods including how bright they appear to be, and with both their speed and distance we can calculate how fast the Universe is expanding.
The farther away you go, the faster the Universe expands, and what Planck found is that the Universe is getting bigger at a rate of 67.3 kilometers per second per megaparsec. A megaparsec is a unit of distance equal to 3.26 million light years (which is convenient to astronomers). That means that if you look at a galaxy one megaparsec away, it appears to be moving away from you at 67.3 km/sec. A galaxy two megaparsecs away would recede at twice that speed, 134.6 km/sec, and so on.
This is called the Hubble constant. Various methods have been used to measure it for the past century, and some of the best found it to be about 74.2 km/s/Mpc. Planck’s measurement is smaller, so the Universe appears to be expanding a little more slowly than we thought, which is why the age is a bit higher than measured before, too.
Part of the reason the number is smaller from Planck is that it’s looking at light that is very old, and came from very far away, so they extrapolate forward in time to see how fast the Universe is growing. Other measurements use light from objects that are closer, and scientists extrapolated backwards.
Since the two numbers are different, this may mean the Hubble constant has changed over time, though that’s way too preliminary to tell. I’ll just note it here as an interesting development. The Hubble constant is notoriously difficult to measure, and I imagine astronomers will be arguing about it for some time yet to come.
The Universe is 4.9 percent normal matter, 26.8 percent dark matter, and 68.3 percent dark energy.
I love this bit. The amount of the fluctuations in the light from the early Universe as well as how they are distributed can be used to figure out what the Universe is made of. The ingredients and amounts of the universal constituents are:
- 4.9 percent normal matter
- 26.8 percent dark matter
- 68.3 percent dark energy
Image credit: ESA/NASA/JPL-Caltech
Normal matter is what we call protons, neutrons, electrons; basically everything you see when you look around. Stars, cashews, dryer lint, and books are all made of normal matter. So are you.
Dark matter is a substance we know exists, but it’s invisible. We see its effects through its gravity, which profoundly alters how galaxies rotate and clusters of galaxies behave. There’s more than five times as much of it as there is normal matter.
Dark energy was only discovered in 1998. It’s very mysterious, but acts like a pressure, increasing the expansion rate of the Universe. We know very little about it other than the fact that it exists, and it’s a bigger component of the universal budget than normal and dark matter combined.
The best estimates for these numbers before Planck were a bit different: 4.6, 24, and 71.4 percent, respectively. That’s neat: there’s less dark energy than we thought, so the Universe is made up a little bit less of that weird stuff, if that makes you feel better. But there’s still a lot of it!
The good news is that having better numbers for all these means astronomers can tune their models a little bit better, and we can understand things a little better. Different models of how the Universe behaves predict different ratios for these ingredients, so getting them focused a bit better means we can see which models work better. We’re learning!
The Universe is lopsided. Just a bit, just a hint, but that has profound implications.
Of all the results announced so far, this may be the most provocative. We expect the Universe to be pretty smooth on large scales. Those early fluctuations should be random, so when you look around at this ancient light, the pattern should be pretty random.
And it is! The distribution of the fluctuations is quite random. It may look to your eye to have patterns, but our brains are miserable at seeing true randomness; we impose order on it. You have to use computers, math, and statistics to measure the distribution to test for true randomness, and the Universe passes the test.
Kindof. The distribution is random, but the amplitudes of the fluctuations are not. Amplitude is how bright they are; like the height of a wave. It’s hard to see by eye, but in the big map made by Planck, the fluctuations are a wee bit brighter than they should be on one side, and a wee bit dimmer on the other. It’s an incredibly small effect, but appears to be real. It was seen in WMAP data and confirmed by Planck.
A simple model of the Universe says that shouldn’t happen. The Universe is lopsided on a vast scale! What can this mean?
Image credit: ESA and the Planck Collaboration
Right now, we don’t know, and there are far more ideas for why this would happen than we have data to test for. It could mean dark energy is changing over time, for example. Another idea, and one that is terribly exciting, is that we’re seeing some pattern imprinted on the Universe from before the Big Bang. I know, that sounds crazy, but it’s not completely crazy. My friend and cosmologist Sean Carroll has some detail on this.
We may be seeing something so big in extent it’s happening over scales we literally cannot see. It’s like having a house built on a slight incline. Standing in one room you might not notice it, but measuring the elevation in a room on one side of the house versus one all the way on the other side might show the discrepancy. And even then, it only gives you a taste of how big that hill might be.
We’re seeing that on a cosmic scale. The Universe itself appears to be slightly canted, and we only get a hint of it when we take the measure the entire Universe.
I am entirely and thoroughly delighted by these new results.
As a scientist, of course, I like it when we get better measurements, more detail, refined numbers. That’s how we test models, and it helps us understand our ideas better.
But I’m human, and a big part of my brain is still reeling from the fact that we can accurately measure the age of the Universe at all. We can figure out what’s in it, even when most of it is something we cannot see. We can determine not only that it’s expanding, but how quickly.
And best of all, we see that the Universe is doing things we still don’t understand. It’s showing us that there is still more out there, things occurring on so vast a canvas that it both crushes utterly our sense of scale and expands ferociously our imagination.
Every day, we get better at learning what the Universe is doing. And the work continues to find out how. It may even lead us to the answer of the ultimate question of all: why?
If that answer exists (if the question even makes sense), and we can understand it, then we are making our first steps toward it right now.
I still hear some people say that science takes the wonder out of life. Those people are utterly and completely wrong.
Science takes us to the wonder.