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I_wonder
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Do cosmologists know what is the current value of the scale factor? I know we have a current value for the Hubble constant H, and I know H=a'/a. But what about the value of a?
Thanks!
Thanks!
cristo said:Usually, the scale factor is normalised so that it takes the value a(t_0)=1 at present times. See this thread https://www.physicsforums.com/showthread.php?t=222284, for example.
BillSaltLake said:R0= 1, which is a dimensionless number. Why? Because I define it as 1. I can define it as any present number I want to, and it will not change the physics. I can arbitrarily define R at one time only; the value at all other times will scale with my choice of R at the single time I selected.
The scale factor, also known as the cosmological scale factor, is a dimensionless quantity that represents the relative expansion or contraction of the universe over time. It is a key parameter in the study of cosmology and is used to measure the expansion rate of the universe.
The scale factor is usually measured using redshift data from distant galaxies. Redshift is a phenomenon where light from an object is stretched to longer wavelengths as it travels through expanding space. This stretching can be used to calculate the scale factor at a given point in time.
The current value of the scale factor is approximately 1. This means that the universe is not currently expanding or contracting, but instead is in a state of equilibrium. However, the scale factor has varied over time and was much smaller in the past and is predicted to continue to increase in the future.
The value of the scale factor is affected by several factors, including the density of matter and energy in the universe, the presence of dark energy, and the overall geometry of the universe. These factors can influence the expansion rate of the universe and, therefore, the value of the scale factor.
The scale factor is essential in understanding the evolution and structure of the universe. It provides a way to measure the expansion rate of the universe and can help us understand the underlying physics and processes that govern the universe's behavior. It also plays a crucial role in various theories and models of the universe, such as the Big Bang theory and the inflationary model.