After seeing the first few minutes of [Veritasium’s](https://www.youtube.com/watch?v=Kp_kqamkYpw) video on how half of the baryonic matter was yet unobserved until recently, he mentions how the ratio of deuterium and helium and other elements were all formed within the first 20-ish minutes after the big bang but also how with around 10 seconds the universe had cooled significantly.
How is that sort of timescale measured accurately when the big bang happened so long ago, especially when even some modern history events cant be traced down to hapening within an exact year sometimes?
In: Physics
Particle accelerators, like CERN. They allow us to run the film backwards, like watching a video of an explosion in reverse.
Those things he talked about in that video weren’t actually measured, they are calculated based on our understanding of physics and our best measurements of the basic characteristics of the universe. In the case of saying when deuterium and helium formed, we know that those elements can’t form above a certain temperature, because we can measure in our particle colliders at what temperature those elements break apart into free neutrons and protons.
Knowing the rate at which the universe is expanding, and knowing the temperature of the cosmic microwave background radiation, we can calculate how hot the universe was at different times in the process of the Big Bang, so we can calculate about when the temperature was low enough that protons and neutrons could stick together to form deuterium and helium. The reason why the time frame is so short (a mere 20 minutes after the actual “bang”), is that the temperature at which protons and neutrons can start to stick together is really, really high. Put another way, it takes a huge amount of energy to pull them apart. The universe was cooling as it expanding, and it very quickly reached a point where there was not enough energy to keep from sticking together.
As for why we can make statements about the first few seconds of the universe’s life when we can’t say for certain how a modern historical event occurred: the model of the Big Bang is based on some pretty well understood physics, and while there was a lot of matter and energy involved, the important factors really boil down to just a couple of things: mainly the density of matter and energy at any given time. For an historical event, you’re dealing with less matter, but the important factors are many times more complicated. You can’t predict how a human being will behave in every situation. If you boil off all that human’s atoms into a gas and keep that gas in a bottle, a physicist can pretty well predict how that gas will behave as you change its temperature and the volume of the bottle. That’s essentially the situation we’re dealing with here.
That said, cosmology is still a developing science. It’s based on our best understanding of how physics works and our best measurements of the basic characteristics of the universe. That said, the fundamental laws of physics aren’t completely understood yet, and the gaps in our knowledge become more important in the first fraction of a second. Also, new observations may end up invalidating or tweaking certain aspects of the story that video told.
I dont think they really can, they just reconstruct through models. Like if you know all the matter was crammed into an area the size of the sun, it would have to behave like xyz, if it was the size of a basketball, it would be abc, etc.
Remember, what scientists are trying to do is the equivalent of coming on a massive smoking crater and trying to reconstruct what was there before the explosion by looking at the pieces they can find.
Using physics you can find out what something will do before it does it. With what we know about physics we can safely assume that different events would have happened at specific times.
The reason events here on earth, more specifically historical events cant be properly timed and dated as accurately is because it isnt all physics.
If we know the Greeks began marching on Troy on Sept 1st, at noon, we dont have enough information to say when they got there. There are a lot of factors in historical events that can make placing it on a timeline difficult. Soldier 1 has the date Sept 1st in his journal. Soldier 2 has Sept 3rd. Soldier 3 says they went in early September but by a different route. And some villager says the Greek army passed her home at the date and time they were allegedly mid battle.
We have 4 accounts here, who is to say which one is correct?
So without video proof, all we have are the accounts of people who are long dead, and people make mistakes, and lie as well. Physics doesn’t.
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