What happened in the early universe?
when the universe
was optically opaque?
in dark sectors?
How could gravitational waves help?
Q: How are they made?
A: By moving mass and energy around quickly.
[cf. electromagnetic waves, made by moving electrons]
Q: How are they measured?
A: They change the proper length $L$ between test
masses, so producing a strain $\Delta
[in fact gravitational waves obey a form of Hooke's
First sign: Hulse-Taylor pulsar
1993 Nobel Prize
Credit: Shane Larson
Orbital decay of Hulse-Taylor pulsar
Solid line - prediction; red dots -
Source: [PD] Wikimedia Commons
LIGO at the Hanford Site
Two black holes merging
Start of GW astrophysics era
Neutron star merger
- Photons arrived 1.7s later, after travelling
140 M ly
⇒ gravitational waves travel at
the speed of light
- Independent measurement of universe's expansion:
- Known luminosity of gravitational waves →
- Telescopes observe host galaxy → redshift; velocity
To look at longer wavelengths,
need to go into
The LISA mission
- Three laser arms,
2.5 M km separation
- ESA led, launching before 2034
- Mission adopted 2017
LISA: astrophysical signals
White dwarf binaries
So what about the GW background?
LISA: GW background
Science Investigation 7.2: Measure, or set upper
limits on, the spectral shape of the cosmological stochastic
Operational Requirement 7.2: Probe a broken
power-law stochastic background from the early Universe as
predicted, for example, by first order phase
Electroweak phase transition
- Process by which the Higgs 'switched on'
- In the Standard Model it is a crossover
- Possible in extensions that it would be first
➥ colliding bubbles then make gravitational waves
via Wikimedia Commons; Morrissey and
Tiny walls to giant bubbles
Fitting everything in is hard
At the cutting edge:
(i.e. most of the energy of the universe
released as latent heat)
- Mark Hindmarsh, Kari Rummukainen
- Oli Gould, Asier Lopez-Eiguren, Tuomas Tenkanen
- Daniel Cutting, Jani Dahl, Lauri Niemi
- Anna Kormu
- Satumaaria Sukuvaara, Essi
- Next few years: GW Cosmology for
- Cutting-edge simulations of the
- Microscale (Monte Carlo) to macroscale (hydro)
- Dark and visible sectors
- After that: The Energy and Gravity Frontiers
- Electroweak phase transition and
CEPC (2030-), ILC (2035-)
- Finnish role in European GW missions:
Einstein Telescope (2030-), LISA (2034-)
- Complementarity between GW and