The Cosmic Microwave Background - 14d - Intro to Astronomy Sessions
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- Опубликовано: 19 окт 2023
- The Cosmic Microwave Background (CMB) is the literal afterglow of the Big Bang and one of our strongest and most detailed pieces of evidence for the Big Bang. We discuss some of its properties.
Full Series Playlist: • Intro to Astronomy Ses...
Please note that this was designed as an introductory survey of astronomy course, mostly for non-science majors, and does simplify many of the topics accordingly. I encourage people who are just getting into astronomy to use this as a jumping off point for more in depth studies. I've tried to edit out specific references to my course (regarding assignments, tests, etc.) but I might have missed some. Finally, scientific fields are constantly advancing, with new data and studies resulting in our ideas being continually improved. This means some of the ideas presented here may soon be out of date, so I again encourage people to continue to investigate whichever topics are of particular interest to you.
Opening Image Credit: www.nasa.gov/feature/goddard/...
I've seen the fuzzy-looking static-like image of the CMB, but I haven't been able to "read" it... anyhow, some thoughts
1. From our knowledge of the universe's history, does it make sense for the very zoomed-out universe to have a web/branch like concentration of matter, instead of just diffuse drops or clumps of matter that look similar at all scales?
2. Could the motion of our detector (including the earth's revolution) doppler-shift the CMB signal?
3. There was a talk in my department briefly mentioning a "cosmic neutrino background". Does it make sense for this to be a thing?
4. How do we know how fast the temperature of the universe's background radiation change in time? maybe the rate of change is not so simple
5. If there are leftover grav waves from the early universe, it makes sense for their magnitude to be greater around the time CMB can be first seen. Can such disturbance of spacetime affect the distribution of matter right now?
6. If we somehow are able to read the spectrum of big bang grav waves, would we obtain the same temperature as the CMB? If not, what's the implication?
7. Along with the CMB, do we also see free electron and protons from the minutes after the big bang? Were all of them bound together as neutral atoms and slow down so much we don't see free electrons/protons flying around?
8. Why do high(low) temperature fluctuations of CMB indicate high(low) density of early matter, instead of low(high) density?
No worries.
Btw, I appreciate how you explain the reasoning of why a theory is accepted... closer to how a scientist thinks than just the science concepts
1. This is an active area of research, looking at how we go from the density distribution we see in the CMB (which isn't the same on all scales, there's a graph on the next video in this series showing how the strength of the fluctuations vary with size) to the web-like structure of galaxies.
2. Yes, we're moving at around 369km/s relative to that CMB rest frame.
3. Yes, and that would have been produced much earlier in the history of the universe. Unfortunately, those neutrinos would currently be at a VERY low energy, so we're not likely to detect it for quite a while.
4. The models are described by general relativity, specifically the Friedmann equations, so if we know the matter/energy composition of the universe we can predict how it will move. An upcoming video will go into some of these ideas (not the math, but some of the concepts).
5. The wavelengths of the gravitational waves from the early universe would be extremely large (larger than galaxy clusters, with periods in the many millions of years), so we'd need to make those observations over that time frame to detect the GW properties (not happening). We need to detect their signal in CMB polarization.
6. The cosmic GW background would have been produced much earlier and would tell us the density distribution of those extremely early eras. This would allow us to test which models can explain how the universe would go from that very early density distribution to the later distributions.
7. The CMB light would have been produced about 379,000 years after the big bang. It look that long for the neutral atoms to form, so we don't have that kind of a signal from the first few minutes (but we can look at the elements produced in the primordial gas clouds).
8. This is an oversimplification, but basically if there is a higher density region (primarily dark matter) producing a deeper gravitational well, then as the ordinary matter falls into those deeper gravitational wells, there's going to be more converted thermal energy.
I often heard that "gravitational waves pass through anything". If it truly doesn't interact with ordinary matter, then it can't do work on matter/there can be no energy exchange.
But we detected gravitational waves.
So there must be an energy exchange (even if extremely minute) between the wave and our instrument. What gives?
They would pass through ALMOST anything, which is what makes them extremely difficult to detect (need them to hit the detector). But they do carry energy and can transfer energy (a minute amount) to the detector.
@@PhysicistMichael with the same logic, would an entire swath of gravitational wave lose energy when passing througy the earth/sun?
@@GeoffryGifari Yes, but by an incredibly miniscule amount. What would be a much more significant effect is that the wavefronts of the gravitational waves would follow the same kinds of paths that light follows (in empty space), so in the same way that light passing by the sun would be deflected (gravitational lensing), the gravitational wavefronts would also be deflected.