Big Bang Evidence Overview - 14c - Intro to Astronomy Sessions
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- Опубликовано: 15 окт 2023
- What testable predictions does the Big Bang model make? What observations have astronomers made that provide evidence for the Big Bang?
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 This means some of the ideas presented here may soon be out of date, so I again encourage people to continue to investigate whichever topics are of particular interest to you.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/...
What i got from your explanation of the "lithium problem" is that we seem to be in an era where advancements in understanding come from scrutinizing discrepancies in detail instead of finding something big that's clearly new
Even though it is a relatively small discrepancy (a factor ~3 compared to the abundances of these different compounds covering a range of a billion) it is large enough that there is something we don't understand either about how a different amount of Li was produced, or if there is some issue with our ability to accurately measure the amount of Li present in the early universe. There are a number of different proposed solutions with various levels of supporting data. So something is going on with that, but it's not the sort of thing that's going to overturn the entire big bang model.
@@PhysicistMichael "omething we don't understand either about how a different amount of Li was produced, or if there is some issue with our ability to accurately measure the amount of Li present in the early universe"
this seems like a place where nuclear-particle physics (what i'm used to) and astrophysics can intersect
Maybe this is covered in another video, but i'm having difficulties grasping how the early universe can be extremely hot yet has very low entropy
This is a bit imprecise, but you can approximately think of entropy as how likely it is for a system to be in a particular state. In a typical gas, if you have part of that gas at a high temp and the rest at a low temp, that's less likely to happen on its own (lower entropy), since heat will quickly and spontaneously flow from the high temperature part to the lower temperature part, and that causes an increase in entropy. But in cases where gravity plays an important part, having a very uniform initial state (which our universe seemed to have) is the state that is very unlikely (low entropy) because if there's a tiny part with a slightly higher density, gravity will quickly pull the material around that together and cause a gravitational collapse (this causes an increase in entropy). So that very uniform initial state has a very low entropy since gravity plays a hugely dominant role.
@@PhysicistMichaelhmmm so instead of imagining hot high entropy gas and cold low entropy perfect crystal (which i did), it is more apt to imagine lets say, our solar system has relatively high entropy because matter are clumped (in stars, planets, asteroids, etc.) and it would have low entropy if the "solar system" is made up of diffuse gas instead?
yeah i often don't include gravity and the large scale of space when trying to visualize entropy
I guess the "non-interacting" assumption of the ideal gas plays into that
on nucleosynthesis, is it possible for heavier elements to be produced in a black hole accretion disk and released out to the wider universe through "jets" (from a previous video), considering how extreme the condition is?
I did a quick search about this and it seems like the more significant affect seems to be rather than the jet of an active galactic nuclei directly driving nucleosynthesis, the jets may introduce more disturbances to the gas in those galaxies, driving star formation, and those stars go through nucleosynthesis and produce the heavier elements for the galaxy.
If the expansion of the universe was somehow much faster/slower before neutral atoms form, the ratio between elements would be different right?
During those early eras, the dynamics of how the universe was expanding was determined by the amount of radiation (photons and fast moving neutrinos). This amount of radiation is fairly well constrained by the properties of the CMB, so the other major factor would be the density of baryonic matter (read ordinary non-dark matter). This is essentially what is on the horizontal axis in the graph at 14:53.
@@PhysicistMichael wait so expansion dynamics is determined by the amount of radiation and not the other way around? or maybe they're deeply intertwined