Where Did the Universe Come From? (2 min)
Kaplan_Universe.mp4
Expanding Universe
Properties of Photons
These horizontal lines represent energy levels within the
hydrogen atom. Greater energy transitions produce shorter
wavelengths. The Balmer series transitions produce spectral
lines in the visible light range (400-700 nm).
Spectral Lines (Continuous)
Spectral Lines (Hydrogen Emission)
Spectral Lines (Hydrogen Absorption)
Not only can we determine the elements and molecules from
these spectrum lines, but from any Doppler shift of those
lines, we can measure the velocities of the source with
respect to us, and, therefore, measure the rotations of
galaxies, the rotations of stars, measure how fast galaxies
are receding away from us and so on.
Cosmic Microwave Background (CMB)
Imprint of Quantum fluctuations?
Baby Picture 382,000 years after the Big Bag
Cosmic Inflation
In the context of cosmic inflation, quantum fluctuations are
speculated to play a crucial role in two main ways:
1. Seeding Structure Formation: Quantum fluctuations during
inflation are stretched to macroscopic scales due to the
rapid expansion. These fluctuations become the seeds for the
large-scale structure of the universe, leading to the
formation of galaxies and clusters.
2. Potentially Triggering Inflation: Some theoretical models
propose that quantum fluctuations could cause the inflaton
field to reach a high-energy state in a localized region.
This fluctuation could push the field over a potential
barrier, initiating inflation in that region—a process
similar to quantum tunneling.
Cosmic inflation explains several key features of the
universe—its flatness, uniformity, and the distribution of
structures—through the idea of a rapid, early expansion.
While direct evidence of inflation (such as the detection of
primordial gravitational waves) is still sought, current
observational data strongly support its predictions.
For example, inflation predicts a specific pattern of
polarization in the CMB called B-mode polarization, which
would be caused by primordial gravitational waves.
A Polarizing Discovery About the Big Bang! (2 min)
Polarizing_Discovery.mp4
In 2014, the BICEP2 experiment claimed to have detected this
signal, but it was later shown to be due to interstellar
dust. However, ongoing experiments (such as CMB-S4) aim to
make this detection, which would provide strong direct
evidence for inflation.
Gravitational Waves
https://physurls.com/?q=gravitational%2Bwaves&btnG=phyurls
Evidence for Inflation
https://arxiv.org/pdf/2407.03577v1
Background Imaging of Cosmic Extragalactic Polarization (BICEP)
http://bicepkeck.org
Measuring the B-modes of CMB polarization is crucial because
they can provide evidence for cosmic inflation through
primordial gravitational waves, map the distribution of dark
matter via gravitational lensing, and test theories of
gravity. Additionally, B-modes help constrain neutrino
masses and offer insights into the Epoch of Reionization,
making them key to understanding the early universe and
fundamental physics.
Gravitational Waves by Monitoring Pulsars
Strong evidence for the discovery of a gravitational wave background
https://www.nature.com/articles/s42254-024-00711-6
Pulsar timing arrays worldwide have provided 2σ–4σ evidence
for the detection of a gravitational wave signal in the form
of a stochastic gravitational wave background consistent
with astrophysical expectations.
By monitoring the deviations in the times of arrival of the
radio frequency pulses of a large number of pulsars for many
years it is possible to measure the gravitational redshift
caused by gravitational waves emitted by far-away sources
and travelling through spacetime between the pulsars and the
Earth.
The signal can be explained in terms of the superposition of
gravitational waves emitted by supermassive black hole
binaries at the centre of galaxies; however, a more
speculative origin, rooted in processes taking place in the
very early Universe, for example at the quantum
chromodynamics energy scale, is not excluded.
An Enormous Gravity ‘Hum’ Moves Through the Universe
https://www.quantamagazine.org/an-enormous-gravity-hum-moves-through-the-universe-20230628/
Science News Media
A new analysis of the South Pole-based telescope’s
observations has all but ruled out several popular models of
inflation.
https://www.symmetrymagazine.org/article/bicep3-tightens-the-bounds-on-cosmic-inflation
Gravitational Waves
https://physurls.com/?q=gravitational%2Bwaves&btnG=phyurls
Early Universe
https://physurls.com/?q=early%2Buniverse&btnG=physurls
The Year in Physics (2024)
https://www.quantamagazine.org/the-year-in-physics-20241217/
Latest Science (all sciences)
http://edu-observatory.org/media/Science/index.html#LATEST
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