Leogulus-Champ's (Taweewat Somboonpanyakul) blog: Comment on Primordial Gravitational Waves by Prof. Daniel Holz

Primordial gravitational waves may have been detected in this swirly pattern of light from the early universe. Image: BICEP2 Collaboration

I took a class called Spacetime and Black Holes during the fall quarter of my third year and the professor for that class was Prof. Daniel Holz. Some of his work also relates to gravitational wave and general relativity. After the announcement of the discovery, he gave us a comment about this latest and most excited finding so far this year about the first direct detection of gravitational waves and how it becomes an evidence for the inflation theory of the early universe. I thought I would like to share this here since we are all in a moment of history where most physics might start to change from this point on.

Dear class,

Hopefully all of you have heard about the absolutely incredible result which was announced earlier this week. Some students have asked me about it, and I thought I'd share with you all some very brief thoughts about the result, and why it's so important.

They have detected gravitational waves in the imprint of the cosmic microwave background radiation. I think there are three reasons this is a huge big deal:

1. This is the first direct detection of gravitational waves. We knew these waves existed through indirect measurements (e.g., binary pulsars), but now we've managed to take an actual picture of a gravitational wave (granted, the picture is ~14 billion years old, and doesn't have much detail; LIGO will eventually give us a video of a gravitational wave passing right next to us). But still, this is a huge big deal.

2. This is consistent with expectations of our theory of inflation. This means that we seem to be observing the result of physics that happened when the Universe was ~10^{-35} seconds old, at an energy scale of ~10^{16} Gev (the LHC is ~10^4 Gev, for comparison). It is astounding that we can infer things about what was happening that early, and at those energies.

3. This shows that general relativity is quantized, i.e., that there must be a theory of quantum gravity. Even ignoring the details of inflation, if we believe the general picture (and it is quite compelling for a variety of reasons), we have to conclude that the waves we are seeing in the CMB were generated from quantum fluctuations of spacetime itself. It is mind-blowing that we can know this.

This blog post provides some of the background about the discovery. For more detail I highly recommend Wayne Hu's webpages.

I think this is one of the most amazing results we've ever had in physics. It's certainly a great time to be thinking about general relativity, particle physics, and cosmology!