The newly announced detection of primordial gravity waves is big news. Here’s why:
PBS Newshour ran a segment called “Evidence of cosmic inflation expands understanding of universe’s origins”, interviewing physicist, cosmologist and author at the California Institute of Technology Sean Carroll. A small segment from the transcript (the site includes the video):
SEAN CARROLL: What it will do is help us as a species understand our place in the cosmos. So, I personally think that that should affect your everyday life. It helps us really appreciate what the universe is, how it behaves. And that has to feed into how we think about ourselves.
GWEN IFILL: So, it informs the way we see our world and our place in the world, in the larger universe?
SEAN CARROLL: Yes, what separates us from merely existing, surviving from day to day is that we are curious. We are creatures that want to understand.
Like Carl Sagan, whose “Cosmos” is back on TV now with Neil deGrasse Tyson, Carl Sagan once said, we are the universe’s way of thinking about itself. We are a collection of atoms and particles, just like the rest of the universe, but we have the power to theorize, to go out there and collect data, and to understand the context, this wonderful universe that we live in.
GWEN IFILL: It sounds almost theological.
SEAN CARROLL: Well, I think it’s a very similar impulse that drives people to theology and to science. You want to understand the bigger picture.
I think that science is different than theology in many ways, one of which is, you have got to make predictions, and if the predictions don’t come true, we throw away your theory. So, the wonderful thing now is that this extrapolation from Alan Guth and collaborators over 30 years ago, somehow, miraculously seemed to get the right answer, and our ability to comprehend our cosmos has been demonstrated once again.
Bishop Nick Knisely (and former physics student) explains the significance of the new data:
What’s been found is the first experimental evidence of a theory that’s been widely accepted but never “proved” by primary data, that very early on in the existence of our Universe, space-time expanded at rate far exceeding the speed of light. We don’t really know why that happened, and we don’t really know for sure that it stopped happening, but the fact that it happened was used to explain the relative homogeneity of matter and energy in the early Universe, and the fact that the space-time manifold is nearly flat.
The “nearly flat” part was the motivation for the original idea behind what’s called the “Inflationary epoch” of the Universe. When I was a physics student back in the mid seventies and mid eighties the big push in observational cosmology was to try to determine whether we lived in an open or closed Universe. A closed Universe would have had a overall curvature of space-time that would be “spherical” in a four-dimensional sort of way – like the two-dimensional surface of the earth is curved in a spherical way in three dimensions. An open Universe would have been curved like a saddle shape. A good chunk of my graduate studies were involved in working out some of the basic mathematics of a curved Universe (specifically: finding coordinates under which the Klein Gordon Equation was separable into individual spatial unit vector terms). We talked about the funny but completely unexpected possibility that the Universe was “flat” – and had exactly zero curvature. That was the Euclidean ideal, but no one executed to find it.
Except we did. The data kept coming in and as it got better and more precise, the observed curvature was shown to be about as perfectly flat as anyone could measure.
That was a big surprise. Of all the infinite values that the Universal curvature could be, the odds of it being exactly flat were vanishingly small. Something must have made it that way.
For more explanation, Knisely points to Carroll’s blog post “Gravitational Waves in the Cosmic Microwave Background”, and to Ethan Siegel’s “Evidence of the Universe From Before the Big Bang?”.