Mini-Science 2015 Q&A: “Seeing the big bang”
At the conclusion of each Mini-Science lecture, audience members submit their questions to the evening’s presenter. If there is not enough time to answer them all on the spot, some of the other unanswered questions are sent to the presenter for posting here. Here are questions from Professor Matt Dobbs’ lecture “Seeing the big bang” (February 25, 2015).
Q: How will knowing more about the start of the universe help us in practical terms in the present and future?
A: There is no direct application presently known for our knowledge of the very early universe, but certainly the technology we develop to observe it will have other applications.
For example, we provided a copy of the electronics and detectors we developed for the South Pole Telescope to a US group for nuclear non-proliferation monitoring. They used it to measure the energy of the gamma rays (light) being produced by a nuclear reactor, and from its energy spectrum, can deduce what’s burning inside. This allows for them to determine if the reactor is being used to breed isotopes like plutonium that can be used for bombs.
Q: What causes the universe to expand? Why can’t particle physics take place in a non-expanding space-time universe? Or does space-time have some inherent expansion property?
A: We are deducing the equations that describe the expansion of the universe, but we don’t know why the equations were set up this way. Being able to produce a “theory of everything” that describes what we see would be a dramatic achievement, though it does not tell us anything about why the equation is the way it is.
Particle physics can take place in a static (non-expanding) universe. Much of what we know about quantum mechanics and electromagnetism was figured out more than 80 years ago when we didn’t yet realize the universe is expanding.
Space time need not expand. In fact, our equations also allow it to contract or even collapse at some later time. Whether or not this happens depends on what the “make up” of the universe is — whether it contains more matter or radiation or dark energy.
Q: You spoke about the early universe having conventional matter. Where did this matter come from?
A: That’s a great question and something we really don’t understand. As a naive guess, any physicist to date would have wagered that the universe contains equal amounts of matter and anti-matter, such that the two could perfectly cancel out to zero matter, giving pure energy only.
But this is not what we observe. We live in a matter dominated universe. If you can explain why, you’ll probably get a Nobel prize.
We do have some mechanisms to create more matter than anti-matter. A process called charge-parity violation, first observed (to the great surprise of many) many decades ago. This mechanism allows an asymmetry, but any way that theorists massage the equations they cannot get an asymmetry that is as big as what we observe in our universe. Some people think that, by studying this asymmetry in the neutrino sector, we may find a key to the answer.