Age of Universe Derived

HaeMaker writes "The age of the universe has been calculated to be 12 Billion years +/- 10%, and the Hubble Constant (the rate at which the universe is expanding), is 70km/s/Mparsec.... or in other words, for every Megaparsec (3.26 Billion Light Years) an object is away from us it is moving 70km/s away from us. So, if a galaxy is 2 megaparsecs away, it is moving at a speed of 140km/s away from us. Here is NASA on the subject. "

Comments

Slight error in post.

[Gruuk]

Just a small correction: a megaparsec is 3.26 million light years, not 3.26 billion.

Take it with a grain of salt..

[Ex-NT-User]

It seems that every few years some new group of researchers "discovers/calculates" the age of the universe. And everytime they recalculate it the universe seems to get older by a few billion years. So I would take this latest calculation with a grain of salt, 'cause I'm certain that in a few more years someone is gona claim that it's 13+ billion years old.

Ex-Nt-User

12 billion years is probably a lower limit

[tim pickering]

the hubble constant is only one of the parameters you need to calculate the age of the universe. the overall mass density (commonly expressed as q_0 = mass density/critical density for collapse) and the cosmological constant (if any) are also needed. the 12 billion years is derived assuming the mass density is equal to the critical density for eventual collapse (a flat universe; q_0 = 1) and no cosmological constant. however, we don't really yet know what the values for these other parameters are, even to within a factor of two. current best estimates favor q_0 less than 1 and a nonzero cosmological constant which can result in ages of 15-20 billion years or more for the universe.

the hubble constant is a hard thing to measure right and it's taken decades of work to get it to within 10%. measuring q_0 and the cosmological constant to a similar precision is decades more away, i think.

tim (i'm not a cosmologist, but i play one at work)

Re:12 billion years is probably a lower limit

[EricWright]

To comment on the previous post... this isn't technically correct.

Capital omega (you try typing one) is the ratio of the overall (mass + energy + cosmological) density divided by the critical density (remember, mass IS energy, E=mc^2). In a flat universe, Omega = 1; closed, Omega > 1; open, Omega 1.

Open means the universe will expand forever, with no limit on the physical size. Flat means the expansion will slow to zero in an infinite amount of time, producing a finite physical size to the universe. Closed means self-gravitation of the universe will win out, halting the expansion of the universe, and causing it to re-collapse, presumbly into a "Big Crunch".


The baryonic matter (massive particles such as protons, neutrons, etc.) and photons (light/energy) are all the stuff we see, and is though to have density of about 0.1-0.3 of the critical density.

The cosmological constant (the was invented, then abandoned by Einstein) is a mathematical embodiment that the "vacuum" of space is not actually empty, but full of energy fluctuations that create particle/anti-particle pairs, which annihilate each other in an incredibly short amount of time. This "zero-point" energy would add to the total mass/energy of the universe, and increase the density.

q_0 is the deceleration parameter, equal to 1/2 for a flat universe. If q_0 > 1/2, the deceleration rate is greater, and the universe is closed. If q_0
The current theory is the the density of baryonic matter and light/energy (Omega_b) and the contribution of the cosmological constant (Omega_Lambda) add up to exactly equal the critical density, Omega_total = 1.

Eric (who just finished a stint as teaching assistant for a class in astrophysics and cosmology).