J. Weir [he/they]
email@example.com - davidjamesweir
This talk: saoghal.net/slides/orientation2020
But before I tell you about my research,
I want to take you back to 2003...
- Stretches and squeezes a ring of matter$\Leftrightarrow$
To see what happened right after the Big Bang, need to study longer wavelengths, need to go into space!
Check out this blog post about what our summer students did this year.
Thanks for all the questions. Hopefully these slides go some way to answering them...
It was pragmatic: I didn't really know exactly what I wanted to work on, but I valued having four years of funding rather than three - more time to learn and work on things is always valuable. In different circumstances (such as in Finland, where funding is not fixed so far in advance) I might have chosen differently.
Not really: I was very fortunate with how things turned out. The one thing I sort-of regret is not moving to a different university between my Master's and PhD. But then, many people have personal reasons for needing to stay where they are for as long as possible, and so I would never tell anyone that they must move.
At the moment, it's quite full of online meetings. Our group has online coffee breaks twice a day, and I try to make it to some of them to see how people are. Now that we all work from home, it's harder to have 'random' interactions with your colleagues, and so even if having lots of online meetings seems tiring, I believe it is a good way of making sure everyone feels included. Hopefully soon we can get back to working in the office, too...
This is a good question: the universe has been getting bigger for a very long time! Although we can't observe it directly, we can infer from observations, such as of the cosmic microwave background, what happened in the early moments of the universe. We also know from the abundance of very light elements that they formed in a dense, compact, homogeneous space.
The evidence all points toward the universe expanding throughout its history, even if it seems hard to imagine.
If the universe is expanding, then yes, space-time is expanding – in a sense they are the same thing.
As for whether time is expanding, well, relativity tells us that is hard to separate out from the other effects. Away from any black holes or other dense objects (even the Earth, although the difference is very small), a clock in any part of the universe will tick at the same rate. Good luck synchronising the clocks though... signals can still only travel at the speed of light.
They're two sides of the same coin, I think. I would roughly say that astrophysics is generally concerned with individual objects or groups of objects, while cosmology is concerned with the universe as a whole.
Some astrophysical measurements (such as how fast distant galaxies are moving away from us) tell us about the nature of the universe, and the structure of the universe today (what astrophysicists observe) is seeded by early universe cosmology.
This is a good question: I don't know. Probably the process which gave rise to the emission of the photons takes a bit longer. You can read more about this observation here on the LIGO collaboration web pages.
Whenever we have a system which has a potential energy, we can add or subtract a constant value everywhere and still have the same physics – so in a sense, the value of the potential energy can be zero if we define it to be, even if its minimum were lower.
Generally, the universe, like any system, will settle to the minimum of its potential. However, we might be in a local minimum of, for example, the Higgs potential energy – with a lower, global minimum that the universe has not reached.