The Universe is ~13.8 Billion Years Old

For Round 2, I will make two arguments: both of which stem from the laws of physics as we understand them. The first argument I put forth pertains to the value of the Hubble constant. According to Hubble's Law, the recession velocity of distant objects is their distance times the Hubble constant - H0, about 71 (km/s)/Mpc (1a)(2). As distance and velocity have a linear correlation as per Hubble's Law, to figure out the age of the universe we must merely ask ourselves how long ago was every galaxy at the same point in space. Time is distance over velocity, and the velocity of galaxies is distance times the Hubble constant. The distances cancel, and we find that the time since the entire Universe was a point - the Big Bang - is 1 over the Hubble constant. The definition of a parsec translates into close to 3.9*10^13 km (1b), so 1/71 Mpc/(km/s) (which is 1/H0) is equivalent to 4.37 *10^17 seconds, or about 13.8 billion years. The second argument I will make relates to the Cosmic Microwave Background. Firstly, we must understand that all objects emit electromagnetic radiation (1b), and the frequency of this radiation is dependent on temperature (1c). For example, humans emit infrared light as we are relatively cool, but hotter objects, like embers in a fire, glow in the visible spectrum. Secondly, apparent wavelength can be shifted if the source or the observer is moving relative to the medium through which the waves propagate. This is called the Doppler Effect, and is why a siren on an emergency vehicle sounds higher pitched when moving towards you and lower when moving away. So, the CMB is the 'first light' of the Universe: the first electromagnetic radiation that was able to propagate through space. As the early universe was very very hot, this radiation had a very very short wavelength - close to the Planck length, the shortest divisible unit of space. The CMB is still around us today, too. We can measure its wavelength by finding the temperature objects naturally cool to in space, which turns out to be around 2.7 K (3) which, through Wien's Law (4), translates into a wavelength of 1.074*10^-3 meters. Using the equation for the Doppler Effect, lambda2=lambda1*((1+beta)/(1-beta))^.5 (4), combined with Hubble's Law, we find that the distance to the origin of the CMB is c(lambda2^2-lambda1^2)/H0(lambda2^2+lambda1^2). This translates into 4225 Mpc, or around 13.78 billion light-years. Because light travels 1 light-year per year (that is, after all, the definition of a light-year), we find that radiation first flooded the Universe 13.78 billion years ago, with the actual origin of the Universe not long before. The correlation between these two described methods as well as other, more complicated, ways of determining the age of the Universe provides strong evidence, based purely on the fundamental laws of physics, for a 13.8 billion year old Universe. Sources: 1. Chaisson, Eric and Steve McMillan. Astronomy Today. 8th ed. Boston: Pearson, 2014. Print. a. page 620 b. page 68 c. page 70 2. Huchra, John. The Hubble Constant. Harvard University, 2008. Web. 8 Aug 2014. 3. The Cosmic Background Radiation. University of Tennessee, 10 Aug. 2000. Web. 8 Aug 2014. 4. Wien's Law. Cornell University, n.d. Web. 8 Aug 2014. 5. Relativistic Doppler Effect. Hyperphysics.edu, 5 Oct. 2010. Web. 8 Aug 2014.