By what equation do physicists use to measure the time before the CMB

In summary, physicists have a good understanding of what happened in the universe at certain temperatures by studying the effects in particle accelerators. However, the equation for measuring the time before the CMB and the universe's temperature at that time is still unknown. The Friedmann equation provides the scale factor as a function of time, and the temperature was dependent on this scale factor. This equation is derived from the Einstein GR equation for a uniform distribution of matter in space. By solving this ordinary differential equation, one can determine the temperature at different times in the past.
  • #1
robertjford80
388
0
I'm reasonably convinced that physicists know what happened in the universe at certain temperatures: just find out what happens when you reach those temperatures in a particle accelerator. I still have yet to come across the equation that measures the time before the CMB and what the universe's temperature was at that time. Most physicists agree that the CMB occurred 379,000 years AB (after the BB). I'm assuming they know this because of an equation. Well, what is it?
 
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  • #2
the Friedmann equation gives the scale factor a(t) as a function of time. Temp depends on a(t).

The dependence is pretty simple back when most of the energy was in the form of radiation---a very hot bath of photons---the temp T(t) just goes as 1/a(t).

So all you have to do is solve the Friedmann equation which is an ordinary differential equation governing the scalefactor a(t).

It is a simplified version derived from the Einstein GR equation for the special case where stuff is uniformly distributed throughout space. Basically all you have is a density rho(t) and the scalefactor a(t) itself.
You normalize a(t) so that = 1 at present. And then you run the model back in time.
 
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  • #3
cool, thanks
 

Related to By what equation do physicists use to measure the time before the CMB

1. What is the CMB and why is it important for measuring time?

The CMB, or Cosmic Microwave Background, is a faint, low-energy radiation that is present throughout the universe. It is important for measuring time because it is the oldest light in the universe, dating back to just 380,000 years after the Big Bang. By studying the CMB, scientists can gain insights into the early stages of the universe and better understand its evolution.

2. How do physicists measure the time before the CMB?

Physicists use a variety of methods to measure the time before the CMB, including analyzing the properties of the CMB itself, studying the expansion rate of the universe, and looking at the abundance of certain elements in the early universe. Each of these methods provides valuable information about the age of the universe and how it has changed over time.

3. Is there a specific equation that physicists use to measure the time before the CMB?

There is not a single equation that can be used to measure the time before the CMB. Instead, physicists use a combination of theories, observations, and mathematical models to estimate the age of the universe and the time before the CMB. These methods are constantly being refined and updated as new data becomes available.

4. Can we accurately determine the time before the CMB?

While there is some uncertainty in the exact age of the universe and the time before the CMB, scientists have been able to make relatively accurate estimates. Currently, the most widely accepted estimate is that the universe is around 13.8 billion years old, with the CMB arising around 380,000 years after the Big Bang. However, as our technology and understanding of the universe improves, these estimates may become even more precise.

5. How does measuring the time before the CMB contribute to our understanding of the universe?

Studying the time before the CMB is crucial for understanding the origins and evolution of the universe. By looking at the properties of the CMB, scientists can gather information about the early stages of the universe, such as its temperature, density, and composition. This information can then be used to test and refine theories about the universe, such as the Big Bang theory, and gain a deeper understanding of our place in the cosmos.

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