Gravitational waves and cosmology

David J. Weir [he/they] - davidjamesweir

This talk:

Before we begin:

About me

  • Associate Professor in Physics
    and Academy Research Fellow
  • In Helsinki (more or less) since my PhD (2011)
  • Originally from Scotland
  • Work on gravitational waves in the early universe
    + processes which make them

But before I tell you about my research,
I want to take you back to 2003...


  • I had no course choice until my 3rd year
    ⇒ very broad, valuable, base of science knowledge
  • Later, when I could, I focussed on theoretical topics:
    • Quantum optics
    • Particle physics
    • Quantum field theory
  • Took history of science and other topics non-credit
    - and nearly started a PhD in history of science
  • My Masters project (pro gradu) was on wetting
    - last minute change to theoretical particle physics

How I got into physics: summer jobs

  • 2003: Condensed Matter, University of St. Andrews
  • 2004: (bummed around, folk music concerts)
  • 2005: Space Physics, Imperial College London
    working on the Cassini space probe 🛰😃
  • 2006: Two summer jobs,
    1. Theoretical Physics, Imperial College London
      working on complex networks
    2. Applied Mathematics, Imperial College London
      studying mathematical modelling of evolution
  • 2007: CERN OpenLab (computing department)
    working on volunteer computing/citizen science

Summer jobs, Masters, PhD ...

  • Supervisors and employers care about you developing into a mature, independent scientist
  • Finding projects: talk to potential supervisors + current students:
    • Is it a nice group to work in?
      (for 3 months? 1 year? 4 years?!)
    • Can you get a summer job?
    • What courses do they suggest?
    • Will someone mentor you?
  • Do try new things and take unexpected turns.

What is a gravitational wave?

- Stretches and squeezes a ring of matter

Sources: Wikimedia; ESA
Source: NASA

Two neutron stars merging

Light and gravitational waves from neutron stars

(CC-BY) ApJ 848 L12 (2017)

Neutron star merger and cosmology

  1. Photons arrived 1.7s later, after travelling 100 M ly
    ⇒ gravitational waves travel at the speed of light
  2. Independent measurement of universe's expansion:
    • Luminosity of gravitational waves → distance
    • Telescopes observe host galaxy → velocity

What happened in the early universe? when the universe was optically opaque? to dark matter?

LISA mission

To see what happened right after the Big Bang, need to study longer wavelengths, need to go into space!

  • Three arms (six lasers), 2.5 M km separation
  • Launch 2034

Source: LISA.

Master's programmes

Thank you! Questions?

David J. Weir - - davidjamesweir