In yesterday’s post, I mentioned that my reaction upon reading a second article about the gravitational wave discovery was, “Yeah, but — huh?” Even after the fifth article, I still had one large, unanswered question: How did the gravitational waves form in the first place?
Every article said something to the effect of “they were formed during inflation,” or “they were formed by inflation,” but none of them said how. I wanted details, because it didn’t make sense to me. If the fabric of space-time was rocketing outward in every direction at a jillion times the speed of light, how could ripples possibly form? Wouldn’t that fabric be pulled tighter than a drum head by the forces propelling it outward?
Today, a quick video from New Scientist gave me the “aha!” moment I wanted. Gravitational waves weren’t formed during inflation — they were formed when inflation ended. When it came to a screeching, smoking stop. Unless every point of the exploding universe reduced its rate of expansion at precisely the same moment and to precisely the same low speed, there would be some parts still moving faster while others had suddenly slowed. And if the outside envelope of the universe slowed first, while the inner parts were still going hell bent for leather, then the space-time fabric would get all rucked up.
Rucked up = ripples. And those ripples would propagate outward as the universe continued to expand at its new, sedate speed. They would stretch and lengthen, but would still retain a recognizable pattern.
I feel so much better now.
Also, I must make one correction to yesterday’s post. I wrote, “These are gravitational waves in the light from the birth of the universe,” but what I should have written was “these are gravitational waves from the birth of the universe.” Because the light itself, the cosmic microwave background, isn’t actually from the Big Bang. The newly-born universe was so freakin’ hot that it was opaque to light until it was about 380,000 years old — still a mere infant, but a whole lot older than it was at the actual moment of inflation. Scientists trying to look past this moment have hit an almost literal wall, beyond which we can’t see a thing. By finding the imprint of gravitational waves on this earliest light, the BICEP team has managed to jump our observable universe back in time from when it was 380,000 years old, to when it was 10-32 seconds old. That by itself is a huge achievement, and one that has been overshadowed by the even bigger achievement of possibly proving inflation theory.