Advances in Probing the Origin of the Universe
Wolfson Research Event 2026
Intertwined space and time
Gravity is not just attraction and movement of bodies — clocks also tick differently.
Notion of speed through both space and time (& total is always the speed of light).
e.g. a second on mountain or satellite (up to speed/altitude) is longer than on earth.
Enduring superior speeds and gravitational forces slows clocks.
GPS would not have today’s accuracy if these effects were not accounted for using theory of General Relativity (GR)
\[ \text{Curvature of spacetime} = \text{Content's energy} \text{ (Einstein, 1915)}\]
Spacetime is a curved sheet
GR’s mathematics suggests we live on a sheet of paper (4D in reality) that bends near massive objects.
Falling toward a planet = going along a slide that leads to it.
A non flat sheet means that travelling in space and time is not the same for all — (curvature).
Everything — planets, black holes, light — follows the curves of spacetime and bends them too.
Stars but not celebrities
Earth is one of 8 planets orbiting the Sun — all in nearly the same plane, same direction.
~same setup for the ~100 billion stars in our galaxy (Milky Way) — at least 1 planet per star on average.
100,000 years to cross the Milky Way at the speed of light.
And the Milky Way is just one of trillions of galaxies.
Our galaxy is a tiny speck in the vast universe (cosmological scales).
Moses in a cosmic sea
The Milky Way belongs to a supercluster of galaxies called Virgo — a million times bigger.
In 1929, Edwin Hubble measured that galaxies move away from us — the further, the fastest.
i.e. distances everywhere become bigger: the universe is expanding.
Within a certain range in Virgo, gravity wins: those galaxies stick with us.
Beyond that, expansion wins: those galaxies drift away.
The content of the universe expands the spacetime sheet on cosmological scales, making the distance between galaxies grow.
The cosmic web
The largest scale we can probe: the cosmic web — 10 million Virgo-like superclusters.
Clear pattern: superclusters clustered via gravity; empty bubbles opened up via expansion.
Matter, light, anything with energy dilates space (GR).
But something is also accelerating that expansion: something with negative pressure.
None of the usual matter or forces allow that: call it dark energy, ~70% of the universe, origin unknown.
The expansion of the universe is accelerating due to a mysterious dark energy that we only understand the effects of.
A backward history of time
Simplest picture: the universe as an inflating balloon.
You (a galaxy) and your friends (galaxies) sit on it. Some hold hands — gravity. Others drift apart — expansion.
Rewind: the balloon shrinks. Matter, light and other energies dissolve into a hot plasma.
People thought the Big Bang was there.
The primordial universe with today’s content has been very small, very hot, and very dense. And before?
Intermezzo: Golf on an expanding green
Distances are measured by light travel — the fastest speed allowed.
Expansion doesn’t move galaxies — it makes the journey longer between them.
Can you imagine playing golf on an expanding green? Sometimes the ball can’t win the race.
Some regions of the universe can never communicate/interact/be correlated because too far apart.
The oldest light in the universe
Planck CMB map’s 0.00001 inhomogeneities (2018)
We still receive microwave signals from the Big-Bang plasma — the CMB — coming from all directions.
Strikingly uniform: same temperature everywhere to 1 part in 100,000.
Yet regions on opposite sides of the sky were too far apart to have ever been in contact at that time.
They must have interacted before the plasma.
The CMB is the main evidence for ‘Inflation’, a pre-Big-Bang era during which big scales went from contact to out of contact very quickly.
Hands-on inflation
Inflation: no known particles or forces — described entirely through GR mathematics via its effects on spacetime.
Like a higher-dimensional being stretching the spacetime sheet everywhere around you.
Inflation was dominated by a type of dark energy — the inflaton — with negative pressure, similar to the one driving today’s expansion.
Magnitude of expansion is unmatched: size x \(10^{138}\), in ~\(10^{-32}\) seconds.
To explain past contact between regions that are now out of contact, we need a pre-Big-Bang era of rapid (exponential) expansion (inflation).
The quantum origin of inhomogeneity
Key difference from today’s expansion/ dark energy: the universe was tiny \(\implies\) quantum effects cannot be ignored.
The sky today is slightly not homogeneous when you zoom in — different numbers of galaxies in different directions or CMB map.
The origin of that small inhomogeneity? quantum physics during inflation.
Nonquantum physics: know mass, position, velocity \(\implies\) predict everything.
Sometimes information is missing \(\implies\) probabilities over scenarios. But that uncertainty is just a lack of knowledge.
The quantum origin of inhomogeneity (continued)
Quantum physics: things have no definite value until measured.
Uncertainty is fundamental — not a lack of information.
Probabilistic dynamics of particles are more complex: need an extra dimension (phase), allowing interference between waves of probabilities.
A wave concentrated in space implies a very spread-out probability for velocity — and vice versa.
Both position and velocity cannot be known precisely at the same time:
-> Quantum uncertainty at play.
The quantum origin of inhomogeneity (continued)
Far back enough: the inflaton universe could be in its lowest energy level — the vacuum.
But quantum vacuum is not empty and has a non-zero jitter of energy (particle-antiparticle pairs popping in and out of existence).
Those fluctuations of energy give rise to inhomogeneities during inflation.
The origin of any inhomogeneity is believed to be the quantum vacuum jitter stretched on cosmological scales by inflation.
My work (II)
- [ongoing] Compute probability of inhomogeneous patterns (how likely to have a given distribution of energy at given points in the sky?)
- [future] Compare with e.g. CMB/galaxy data/primordial gravitational waves
Planck CMB map (2018)
DESI galaxy map (2026)
See LISA and Einstein Telescope (2030+) for primordial gravitational waves.
Keep the model/theory which predicts the closest pattern to data