If I understood correctly, the CMB originated at a time when the universe was much hotter and denser than today, and originally consisted of photons of much shorter wavelength than today. As the universe expanded and cooled, the photons comprising this background radiation did too, and at present it appears to us in the microwave range of wavelengths.
I don't understand how the law of conservation of energy holds for the total amount of energy carried by the CMB. The number of photons comprising the CMB can't increase. It can only remain the same or decrease (some photons will get absorbed by matter), and their wavelength is continually increasing. The total amount of energy carried by the CMB should therefore decrease (photons will longer wavelengths have less energy). If energy is conserved, where did this energy go?
I guess I'm just asking because I have no sense of scale when looking at the CMB. Like how large is the average clump? Galaxy-size? Yellow dwarf-size? Great Wall-size? Bigger? I know none of these things existed yet, but I'm just asking about sheer scale here. If all that light was once radiated toward us as the center of our arbitrarily-located observable sphere of the cosmos, how big was that sphere at the time its light was emitted? About 13.7 billion years ago I believe.
Also, since photons are destroyed when detected, will we eventually run out?
We are a bunch of cosmologists from the Cosmology from Home 2020 conference. Ask us anything, from our daily research to the organization of a large conference during COVID19! We have some special experts on
- Inflation: The mind-bogglingly fast expansion of the Universe in a fraction of the first second. It turned tiny quantum fluctuation into the seeds for the galaxies and clusters we see today
- The Cosmic Microwave background: The radiation reaching us from a few hundred thousand years after the Big Bang. It shows us how our universe was like, 13.4 billion years ago
- Large Scale Structure: Matter in the Universe forms a "cosmic web" with clusters, filaments and voids. The positions of galaxies in the sky shows imprints of the physics in the early universe
- Dark Matter: Most matter in the universe seems to be "Dark Matter", i.e. not noticeable through any means except for its effect on light and other matter via gravity
- Gravitational Lensing: Matter in the universe bends the path of light. This allows us to "see" the (invisible) dark matter in the Universe and how it is distributed
- And ask anything else you want to know!
Answering your questions tonight are
- Alexandre Adler: u/bachpropagate Iβm a PhD student in cosmology at Stockholm University. I mainly work on modeling sources of systematic errors for cosmic microwave background polarization experiments. You can find me on twitter @BachPropagate.
- Alex Gough: u/acwgough PhD student: Analytic techniques for studying clustering into the nonlinear regime, and on how to develop clever statistics to extract cosmological information. Previous work on modelling galactic foregrounds for CMB physics. Twitter: @acwgough.
- Arthur Tsang: u/onymous_ocelot Strong gravitational lensing and how we can use perturbations in lensed images to learn more about dark matter at smaller scales.
- Benjamin Wallisch: Cosmological probes of particle physics, neutrinos, early universe, cosmological probes of inflation, cosmic microwave background, large-scale structure of the universe.
- Giulia Giannini: u/astrowberries PhD student at IFAE in Spain. Studies weak lensing of distant galaxies as cosmological probes of dark energy.
- Hayley Macpherson: u/cosmohay. Numerical (and general) relativity, and cosmological simulations of large-scale structure formation
- Katie Mack: u/astro_katie. cosmology, dark matter, early universe, black holes, galaxy formation, end of universe
- Robert Lilow: (theoretical models for the)
When we see light from the CMB, where is it coming from? What actually are we seeing?
I have a 3-tier question (I guess because they're related) but basically:
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Do photons of light "grow" longer in their wavelength over time? (If they dont collide with anything - re: red shift)
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And if 1 is true, does that mean that the microwave photons in the Cosmic Microwave Background used to have smaller wavelengths, thus, the CMB at some point was all in the visible light spectrum?
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If that was true, could our early universe CMB have been a sea of gamma rays? Like some cosmic sea of destruction?
I recently read on the Genius app that John McCrea is referring to the cosmic microwave background in the opening verse to Frank Sinatra. As a huge fan of astronomy and all other things the universe, I thought that it is awesome and the interpretation makes perfect sense. Iβm surprised I didnβt catch it before. Is this news to anyone else?
We are a bunch of cosmologists from the Cosmology from Home 2021 conference. Ask us anything, from our daily research to the organization of a large conference during COVID19!
We have some special experts on
- Inflation: The mind-bogglingly fast expansion of the Universe in a fraction of the first second. It turned tiny quantum fluctuation into the seeds for the galaxies and clusters we see today
- The Cosmic Microwave background: The radiation reaching us from a few hundred thousand years after the Big Bang. It shows us how our universe was like, 13.4 billion years ago
- Large Scale Structure: Matter in the Universe forms a "cosmic web" with clusters, filaments and voids. The positions of galaxies in the sky shows imprints of the physics in the early universe
- Dark Matter: Most matter in the universe seems to be "Dark Matter", i.e. not noticeable through any means except for its effect on light and other matter via gravity
- Dark Energy: The unknown force causing the universe's expansion to accelerate today
- "The Hubble Tension": Measurements of the universe's expansion rate, which are almost identical but, mysteriously, slightly discrepant (aka the [sigh] "crisis in cosmology")
And ask anything else you want to know!
Those of us answering your questions tonight will include
- Alex Gough: u/acwgough PhD student: Analytic techniques for studying clustering into the nonlinear regime, and on how to develop clever statistics to extract cosmological information. Previous work on modelling galactic foregrounds for CMB physics. Twitter: @acwgough.
- Katie Mack: u/astro_katie cosmology, dark matter, early universe, black holes, galaxy formation, end of universe Twitter: @AstroKatie
- Shaun Hotchkiss: u/just_shaun large scale structure, fuzzy dark matter, compact object in the early universe, inflation. Twitter: @just_shaun
- Tijmen de Haan: u/tijmen-cosmologist McGill University: Experimental cosmology, galaxy clusters, South Pole Telescope, LiteBIRD
- Rachael Beaton: u/rareflwr41 Hubble Constant, Supernovae, Distances, Stars, Starstuff
- Ali Rida Khalife: u/A-R-Khalifeh Dark Energy, Neutrinos, Neutrinos in the curved universe
- Benjamin Wallisch: u/cosmo-ben Neutrinos, dark matter, cosmological probes of particle physics, early universe, probes of inflation, cosmic microwave background, large-scale structure of the universe.
- Ashley Wilkins u/cosmo_ash PhD Student Stochastic Inflation, Primordial Black Holes and the Renormalisation Group
- Charis K. Poon
