Gravitational waves and cosmology

David J. Weir [they/he] - davidjamesweir

This talk:

Before we begin:

About me

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...


  • 2002-2003 University of Edinburgh
    (dropped out)
  • 2003-2011 Imperial College London
    MSci, PhD (eight years in one building!)


  • 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 ...

  • Don't rush your studies
    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.

Key takeaways:

  • Listen to:
    • Potential employers
    • Senior students
    • Mentors
    • Supervisors
  • Faster doesn't mean better. Don't rush your studies.
  • Interests + connections you develop will matter.
  • Be broad now, you can be narrow later
    ☞ Don't miss out on your new favourite thing.

About gravitational waves and cosmology

What is a gravitational wave?

- Stretches and squeezes a ring of matter

Sources: Wikimedia; ESA

First evidence: Hulse-Taylor pulsar

Source: Shane L. Larson

Hulse-Taylor pulsar

  • Two neutron stars, of which at least one pulsar
  • Orbital diameter: 3 light seconds
  • Orbital period: 7.75 hours
  • Orbit slowly contracting (3.5 metres per year)
  • Energy must be going somewhere...
    gravitational waves
  • Gravitational wave power output: $7\times 10^{24} \, \mathrm{W}$
    (about 2% of the Sun's EM radiation).
Source: NASA
Source: (CC-BY) Andrea Nguyen on Flickr

LIGO at the Hanford Site

Source: (CC-BY-NC-ND) Prachatai

Two neutron stars merging

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

Thank you!

Next up: Anna Kormu

Anna will talk about LISA and working with us!

Ask questions anonymously of both of us: