The Latest News From The Big Bang

It won’t make you richer. It won’t organize your calendar. It probably has no practical application whatsoever. But the scientific discovery announced on March 17th is one of the great discoveries of the new century, and virtually certain to result in a Nobel Prize. (Appropriate note of caution: assuming this is confirmed and stands up to peer review.) Here is a link to an article by Dennis Overbye, the long-time science writer for the New York Times.

In the question-and-answer format that follows, I’ll try to explain what the new discovery reveals and what was actually discovered. I hope it will neither annoy those who really, really know this stuff nor blow away those whose last science course was in high school! Get comfortable and settle back, because this will take a while. Maybe set aside two sessions.

What exactly was discovered?

Patterns in the polarization of radiation from the cosmic microwave background (CMB). Yeah, I know—geek talk. Let’s try and break that down to standard English.

In the early 1960s, two competing cosmological theories stood on roughly equal ground. Steady State theory acknowledged the expansion of the universe that had been detected decades earlier, but it still maintained that the overall universe did not change with time. “Continuous creation” filled in the gaps left by universal expansion; the universe billions of years ago and billions of years from now would not look any different over galactic scales of distance.

Steady State

The competing Big Bang theory discarded the idea of continuous creation, and asserted that the expansion meant that the average separation between galaxies would be greater five billion years from now than it is now. More to the point, the theory “ran the clock backward” to a hot early universe that was much smaller than today’s.  The average separation of galaxies would increase over time.

Big Bang

A successful scientific theory is one that makes testable predictions. A hot early universe would have cooled as it expanded, not by radiating heat away like a coffee cup, because there is nothing to radiate it away to–there is no “away”. You just have the same amount of energy distributed throughout a much larger universe. A universe with an average temperature of 3000 K expands by a factor of 1000, and its average temperature becomes 3 K.

How did they find this?

So how do you take the temperature of the universe? Well, this won’t do it.

This is more like it.

The upward-facing dish at the right is the BICEP2 radio telescope at the South Pole, which made the measurements we’re referring to.

You know how something really hot can glow in visible light? Like this?

What you may not realize is that anything whose temperature is above absolute zero emits light. It’s just that cooler objects emit “light” of lower energy and longer wavelengths. You are quite bright in invisible infrared light, something that lets firefighters find people even in dense smoke.

An object—or a universe—at 3 K (3 degrees above absolute zero) emits low-energy microwave radiation. In 1964, two scientists trying to reduce background noise in satellite transmissions found this radiation in every direction they pointed their antenna. This is the cosmic microwave background (CMB), which lent very strong evidence to the Big Bang Theory, effectively killed the Steady State Theory, and earned those two scientists a Nobel Prize in 1978. And that’s what this radio telescope is designed to detect.

Why in the world would you build a radio telescope at the South Pole?

Microwaves are absorbed by water vapor in the atmosphere, so the higher (less atmosphere to look through) and drier (low humidity) and clearer (hardly ever any clouds) the better.  The South Pole qualifies beautifully on all counts.

But I thought you said something about patterns and polarization.

Yeah, about that. Let’s see if we can explain polarization first. You’re probably familiar with the depiction of light as a series of waves, with different colors having different wavelengths.

Microwave radiation has a much longer wavelength than visible light but is otherwise just as depicted in the diagram.  Unpolarized radiation vibrates in all different directions, like this:

But polarized radiation can be detected by seeing if it passes through a polarizing filter. Think of the filter as a picket fence.

And this is where I’ve decided not to go much deeper. There are different types of polarization from different causes, and if you decide you want to go that deep, here is a good source for that, from an article posted last summer.

Here is a representation of what this pattern looks like.

Much more subtle and difficult to detect than this image would suggest.

So what does it mean?

These particular patterns have long been predicted to result from gravitational waves, a so-far-unobserved prediction of Einstein’s century-old General Theory of Relativity. This is best thought of as a theory of how gravity actually works, and rather than sidetrack into a lengthy description, let’s just give a general idea of how one generates gravitational waves by thinking about how one generates electromagnetic waves. A radio transmitter does so by moving things that are charged. Electrons moving in a transmitting antenna generate electromagnetic waves. Generating electromagnetic waves isn’t that hard—you do it every time you heat your dinner in a microwave oven.

Generating gravitational waves is a lot harder because gravity is so much weaker than electromagnetism. These waves are generated by moving mass—and you have to move a LOT of mass BY a lot to generate gravitational waves strong enough to be detectable.

The new discovery doesn’t exactly (as some early reports suggested) help confirm the Big Bang Theory so much as it lends strong evidence to one particular aspect of the theory. To help explain some troubling observations that seemed incompatible with the theory as it existed then, Alan Guth in 1980 proposed that in the very earliest instants after the Big Bang, the universe expanded at an almost inconceivable rate, then slowed down to a relatively more sedate pace. This definitely amounts to moving a lot of mass (the whole universe!) by a lot, and would have generated those gravitational waves. Andrei Linde solved some of the inconsistencies in Guth’s original proposal, and of course theoretical work augmented by observation has been ongoing since then. These latest observations are a beautiful example of a theory being borne out by evidence.

So who gets the Nobel?

Since I’m not a member of the Royal Swedish Academy of Sciences, I don’t have a say! But Guth is probably the surest bet, closely followed by Linde.  If the Swedes want to add a third person (the award cannot be given to more than three persons), then John Kovac (the leader of the observational team) seems the logical choice to me.

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Posted in Cosmology

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