Being able to see single stars in other galaxies wasn't just good for proving that galaxies were far, far away. It also proved just how far away they are. Some stars don't burn with a steady light, but they wobble bright, then dim, then bright, then dim, so regularly that you could set your watch to the oscillations. It’s almost as if the stars are breathing in and out. The first person to notice this was a computer: one named Henrietta Swan Levitt to be precise.
(A hundred years ago, Harvard College Observatory hired roomfuls of technicians to process and catalogue the photographic plates that came from the telescopes. Most of these “computers” were women because an early director found they could do the job as well or better than male assistants, and, unjustly, for half of the going rate as the men. Part of Harvard's reputation today must be attributed to the work of these unsung heroes.)
Levitt discovered this regular pattern of star-breathing when she was looking at the constellation Cepheus, so this special kind of star is called a Cepheid. The oscillations are so unnervingly regular they can be used like marks on a ruler to measure how far away each star is. This is how, for instance, the size of the Milky Way was figured out, which so impressed everyone at first, but turned out to be the mere tip of the iceberg. Hubble used Cepheids in distant galaxies to calculate the exact number of “reallys” you have to put in front of “really far away” for his galaxies (assuming a conversion factor of 1000000 kilometers per “really”, of course). This, even more than actually seeing the stars, is what convinced everyone that these clouds were massive and far away, not just splotches of dust.
If you can learn a lot about the size of the universe from looking at the intensity of light, imagine what you can learn from looking at its color! Once bigger and better telescopes allowed us to look at colors of galaxies farther and farther away, these colors started to tell us something hugely important. The farther away the galaxy, the redder it appears, without fail. This is strange, because galaxies should be pretty much the same color, or perhaps if they differed they'd be mixed up in color like a jar of assorted jelly beans. But they only differ based on distance.
An important clue for how this could be comes from Albert Einstein’s Theory of Relativity. Don't be fooled by the name: this is actually a theory of absoluteness, because everything in it springs from the one statement that nothing can go faster than light. There is an absolute speed limit to the universe, set to the speed of light itself. (We’ll get to the “relative” part in a few paragraphs.) Light’s speed is absolute, everywhere, everywhen. As a result, if you’re moving away from something that’s glowing, the speed of the light won’t change but its color will. Specifically, it will look reddish, and the faster it’s moving away, the redder it will look. (You’ve never observed this effect in person because, no matter how fast that 1978 Toyota I bought you goes, you’ve never come close to moving at the speed of light. Try and you're grounded.)
This “red shift” is amazingly consistent. When we look around ,we see all galaxies outside of our local cluster running backwards, away from us. The farther away from us, the faster they're going. It’s a bit like being at a crowded party and then realizing that everyone is inching backwards away from you (if it’s any comfort, everyone is also inching away from everyone else). Or as if you’re standing in a room, and you look north, south, east, west, up, and down, and every wall is rushing away from you. Think the entry rooms to Disney's Haunted Mansion on a grand scale.
This gave the scientific community an immediate sense of vertigo. No wonder they developed a sense of nausea. Hubble played a role in putting together the data, and got his name put on the observed “red shift,” but he didn’t really put it together to figure out what it all meant; it was just too weird for him. It took a priest with a Ph.D. from MIT named Georges Lemaitre to say what's probably occurred to you already, “So if everything’s moving away from everything else, doesn’t it follow that at first everything was together, at a single point?” This is just a case of playing “connect the dots” with galaxies and realizing all trajectories meet at a single point. Lemaitre called it a “primeval atom," which, as Dave Barry would say, sounds like a great name for a rock band. The universe is an inflating balloon, with the galaxies as specks painted on its surface. And it’s still blowing up and out. (Sam, there’s your balloon, as promised.)
The very idea that the universe was once mashed down into a single point seemed preposterous to scientists brought up on the Greek idea of a static or flat universe. Fred Hoyle, a brilliant scientist in other respects but one of the leading proponents of the “Steady-State Theory” that insisted something else must be wrong, scornfully called this primeval explosion the “Big Bang.” But the name stuck, and is now the name everyone uses!
It's important to keep in mind that this has all changed in the last hundred years. More experiments in the 1960’s helped the case of the Big Bang theory. Two scientists from Bell Labs were trying to use microwaves to carry phone messages, but they heard a constant annoying static buzz below everything. No matter what they did to clean out their system, the buzz persisted. Then they talked to some astronomers down the road: it turns out one of the predictions of the Big Bang theory is that there should be a constant, low-level “echo” of microwaves in the universe. That is what they were hearing. You can see some for yourself if you tune a TV to an unused channel: about 1% of the static you see is from this background radiation. The exact properties of the static they measured matched what the Big Bang model said we should "hear" at that frequency. (Their measurement is the blue bar on the left side of the blue-and-pink graph below, by the way.) But it was just one point -- and it would take a satellite to measure many more.
The microwave static helped to cement the case for the Big Bang, but the Bell Labs experiment could only see a fraction of the radiation that the Big Bang caused. A satellite was designed called the Cosmic Background Explorer (COBE) that could better observe the shape of the radiation, from its vantage point in orbit far above the interfering veil of the atmosphere. It was able to systematically scan microwaves from every part of the sky that had never been compared before. A simple event like the Big Bang should produce a simple pattern of microwaves, evenly spread out through the sky. What it saw was this, colored from red to blue over a span equivalent to four degrees Celsius:
Hmmm. Looks pretty simple to me. The reasons for this are pretty complicated, but basically, a big explosion that started the universe should leave a big, even residue of microwaves spread across the universe. And that's what we see!
Better than colors, let's use numbers. If you draw a graph, you can put the prediction of the Big Bang theory on it as a line, and the measurements that we’ve got can be put as points near that line. The better they line up, the better the theory. See for yourself (blue dots are from COBE, and see how they match the pink line exactly):
[both pictures from http://ircamera.as.arizona.edu/NatSci102/lectures/bigbang.htm]
The blue points match the pink line as if they belong there. Therefore, the Big Bang is currently one of the best-proved theories in physics. Since COBE, physicists have learned to accept it.
So we’ve established that there was a Big Bang event. What does it mean? It means if we run the film backwards, we see the birth of the universe, and this expansion started from a point. So all this bigness was contained in something smaller than small. It was nothing.
There was a void. God said let there be light. And there was light. That’s not a bad description of what happened. The universe was wound up like a clock, and exploded like fireworks, or the beginning of Star Wars theme music. There was a starting line to a grand race of galaxies when everything was compressed like a tiny springy snake in a peanut brittle can, waiting to be unleashed. I can try with mixed metaphors like these, but I can't improve on what I hear in the Bible, with ears and eyes that have taken in what science has to give me. I really think that knowledge of Genesis 1 allowed Lemaitre to see what the data meant, and to name the beginning of everything.
By everything, I do mean every thing. Don’t forget that we may be talking about the beginning of space, but we’re also talking about the beginning of time. It’s easy to think of time the way the ancient Greeks thought of the universe: constant, static, even flat. But that is a mistake. According to physicists, time is a fourth dimension that goes along with the three space-dimensions of height, width, and breadth. "Our instinct is to regard time as eternal, absolute, immutable -- nothing can disturb its steady tick. In fact, according to Einstein, time is variable and ever changing. It even has shape. It is bound up -- 'inextricably interconnected,' in Stephen Hawking's expression -- with the three dimensions of space in a curious dimension known as spacetime." -- Bill Bryson, A Short History of Nearly Everything, p. 126. If the three other dimensions had an origin in the Big Bang, then time did as well.
In the Theory of Relativity, Einstein said if the speed of light is always absolute, then other things have to change, time and space in particular. (This is your mind-bending physics nugget for this post; why should time be able to change when light cannot? The key is that you can't work out the math for light changing, but you can for time changing. Weird, huh?) When I hear “let there be light,” I imagine light as the absolute into which everything else, even time, must fit. It is the laser level against which the universe is squared. The “relativity” that Einstein talked about forces us, humans looking at the past of the universe, to understand that time and space are relative (while light was not) and were compacted in a single origin, so that light itself may remain unchanged, insurpassable, framing the universe and giving us the chance to see things as they are: 10,000 galaxies in a speck of sky flying away so fast they've turned red.
In the past century, science has earned its Creation Myth: it tells us "And there was light." Space and time had an origin. In Genesis 1 we hear the words "Let there be light" and as Christians, we hear the Originator, birthing the universe with his word.
So there was light. There was evening, and there was morning. The first day was done.
[to be continued with Day 2]
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4 comments:
How does the clock-like regularity of star oscillations allow us to tell the distance of a star? Does the speed of retreating stars, in addition to causing the red-shift, also make the oscillations seem slower, making the oscillations of near stars faster than those of far stars?
That's pretty much my broad-overview understanding of it. To be specific, the Cepheid oscillations have a "Period-Luminosity relationship", which means the speed of the wobble and brightness of the star are directly related. This lets you see whether a dim star is dim because it's far away or dim because it doesn't glow as much as other stars (put another way, it allows us to see whether the star is (a) close and dim, or (b) far and bright so it just looks dim).
The red shift is actually a propetry of all light from the galaxy, I believe, so it can be seen with Cepheids (when they can be seen) or with any other kind of light. I described its effect on the Cepheids to keep the explanation a little simpler, and probably made a few mistakes along the way! But it works on all light because all light is an oscillation deep down, so the retreating stars make the oscillations seem slower, exactly like you said.
If you think of yourself sitting on a moving subway where someone drew a wiggly line on the tunnel wall, you can imagine how the wiggle would look different because you're moving. That's exactly what you described for red-shift.
Bottom line is, you need Cepheids to determine distance (at least without more complicated techniques), but you just need light to determine "red shift". Since Cepheids have light, I just used them as an example of both experiments.
Little note to everyone: I've expanded a little bit about the Theory of Relativity and microwave radiation in the second half of this post, because of readers' contributions/questions -- thanks for letting me know so I can try different ways of putting things, or expand on certain points!
Nate,
Not a scientist, but I took astronomy and saw a youtube yesterday that explained this (and I stayed at a Holiday Inn last night):
Scientists found a Cepheid star with a ring of "dust" around it, which was illuminated in oscillation by the star. By timing the delay in oscillation from the star to the ring cloud (and knowing the speed of light) they could determine exactly how far away from the star the cloud was, and thus the exact size of the system. Then simply measuring the subtended angle of this object in our sky and applying a little trig, they could determine the size of that system.
I watched so many vids yesterday, I cant find the one that had this info, and clearly it doesn't work for all Cepheids. The method you described also works and is probably more common, the example above, I believe, was more of a calibration exercise.
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