Hubble Constant
Hubble Constant
This is interesting because there is some disagreement about its value.
The Hubble Constant is the speed at which the universe is expanding. There are two methods available to determine this constant. One is by measuring the red shift of galaxies that exhibit Type 1a supernovae.
The law is given as v = HoD. Ho is the Hubble Constant and D is the proper distance to a galaxy. The D value can change over time, but the velocity v doesn't. Which means that the Hubble Constant may not be a constant.
As I've explained before, Type 1a supernovae always give off the same amount of light, thus making this type of supernovae a standard candle to determine distance. Red shift is what happens to the light from a distant galaxy that's moving away from us. It's caused by the Doppler shift of light. Astronomers have made many measurements like this to determine the rate of expansion of the universe.
The second method involves using the WMAP, which is the Wilkinson Microwave Anisotropy Probe. This space probe measures the differences in temperature across the sky to produce the cosmic microwave background, which is the radiant heat remaining from the Big Bang. This probe has helped cosmologists determine the Standard Model of Cosmology, which determines the age of universe. The current value is 13.772 billion years + or – 0.059 billion years.
The Hubble constant as determined from the first method is 73.8 km/sec/Mpc. (Mpc is mega parsecs). This is good to + or – 2.4 km/sec/Mpc. The Hubble constant from the WMAP is 70.0 km/sec/Mpc good to + or – 2.2 km/sec/Mpc. Why the difference?
First of all, one must realize that the Hubble constant has undergone several changes over the years. In other words there is a lot of discrepancies in these values, and there is a lot of argument going on about why there are these differences.
One possibility is that we don't yet know how much matter and energy is in the universe. This could be caused by the fact that the amount of dark matter and energy is changing over billions of years.
My take on this is that this concept will change with time because better measurements will be made and new theories will develop. It's the way science works. Nothing is absolute.
Thanks for reading.
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