How Long has our Universe Existed and what is the Fate of our Universe?

 A Little Bit about the Age of our Universe:

The Wilkinson Microwave Anisotropy Probe (WMAP) satellite helped us measure our Universe by determining the parameters with an accuracy of better than 1.5%. Therefore, with the WMAP, we were able to estimate the age of the universe to about 13.77 billion years old.

How was the WMAP able to determine our universe at this age?

Since we know the density of the energy and matter of the universe, we can use Einstein's General Relativity to compute how fast our universe was expanding in the past.

We can then take a look back and determine when the universe had "zero" size, according to Einstein. The time between then and now is the age of the universe.

The studies of thermodynamics:

Formalized in the 19th century was the study of thermodynamics. It lead us to concluded theories telling us that the age of our universe was finite. The idea of entropy dictates that if the universe were infinitely old, then everything inside the universe would be the same temperature resulting in no stars and no life.

At this time, no scientific explanation for this contradiction was put forth. Albert Einstein published the theory of general relativity. Following in 1917, he constructed the first cosmological model based on his theory.

Einstein added the cosmological constant to his equations later on in order to remain consistent with a steady state universe, Alexander Friedmann and independently five years later Georges Lemître, showed that the universe cannot be static and must be either expanding or contracting. Einstein's model of a static universe was in addition proved unstable by Arthur Eddington.

Studies suggest that our universe is predicted to end in just five billion years -- coincidentally, close to when the sun is predicted to die. This prediction derives from the theory of eternal inflation, which suggests the universe is part of the multiverse. The multiverse structure is made up of an infinite number of universes that also have daughter universes,’ It impossible to calculate the exact numbers and predictions though due to everything having infinite amounts.