Our Universe is exceedingly mysterious. Everyone knows about it, but no one really understands it. I’m Julia Margie, your host today, as we take a closer look at the birth, life, and probable deaths of our universe. Scientists think that our universe began with a singularity. Then, it expanded. And kept expanding. And now, 13.77 billion years later, it is still expanding. We know this because the light being received from distant galaxies is red shifting, the frequency of the waves of light we are receiving is going down. Another support of the Big Bang Theory is the Cosmological Principle, which posits that, basically, if someone with appropriately bad vision looked at the universe, everything would look approximately the same. Scientists describe this using the words homogeneous and isotropic. This theory is r actually being tested continuously as we analyze the universe and its galaxies at larger scales. A third proof is Cosmic Microwave Background Radiation, which is the remnant heat from the Big Bang. It has a uniform temperature, which means the gas and matter that emitted the radiation in the past was evenly distributed. This theory explains the “Standard Model”, a generally accepted theory that says everything in the universe is made from a few fundamental particles and governed by a few fundamental forces. Using this, about 71.4% of the universe is dark energy, 24% is dark matter and 4.6% is matter. Dark energy is like an anti-gravity, in that it is making the universe expand. Dark matter is matter that we cannot see, touch, or sense because it doesn’t interact with the strong force or the electromagnetic force. We know it is there because the amount of warping from gravitational lensing is too much for just a galaxy to make. There has to be more matter contributing. Gravitational lensing is the distortion of photons by the gravity around large objects. Essentially, spacetime curves and the light follows. Scientists are pretty sure dark matter is non-baryonic, meaning it isn’t made of the protons, neutrons, and electrons that we know of.In our universe today, the average density of matter uniquely determines overall geometry. There is a specific density that means the universe is flat: 5-6 hydrogen atoms per cubic meter. If the average density of the entire universe is less than this “critical density”, then the universe is most likely open and infinite. If the average density of the entire universe is greater than this critical density, then the universe is closed and finite, like a sphere. And, if the density is exactly equal to the critical density, the universe is most likely flat and infinite. Interestingly, it is getting more and more likely that the average density of the entire universe is almost exactly the critical density. One confusing part of this is our definition of flat: 2d. However, we must think of flat as meaning “a plane in which Euclidean geometry (the type we learn in school) is true. Cubes have right angles and parallel lines don’t intersect. We cannot imagine a 3d shape which is flat.There are two ways scientists measure the average density: the accounting approach and the geometric approach. The accounting approach involves estimating the mass of a given (large) volume of the Universe by measuring the masses of objects within the volume. The object’s masses are estimated directly by the measurement of kinematic properties such as galaxy motions within clusters. They can also be indirectly estimated by assuming a relation between the luminosities and masses of individual galaxies within the volume. This method is less accurate because we don’t have much knowledge on the fraction of dark matter in and around galaxies, and the gravitational pull of dark matter affects these movements as well as contributing to the total mass.The geometric approach uses converging and diverging parallel lines. If the universe is closed, the parallel lines will meet. The observed density of galaxies will be less than expected from extrapolating the local densities of galaxies many years ago. If the universe is open the parallel lines will diverge and the observed density of distant galaxies will be larger than suspected. Robert Frost once said: “Some say the world will end in fire, others say ice”. Coincidentally, that describes the scientific end of the universe as well as the poetic. The end of the universe will depend on the universe’s overall shape or geometry, how much dark energy there is, and the “equation of state” (which basically figures out how the density of the dark energy responds to the expansion of the universe). There are three theories in testing: the Big Rip, the Big Crunch, and the Big Freeze. The Big Rip is an end in which the rate of expansion may eventually tear the Universe apart, forcing it to end. Basically, the pull of the Universe’s expansion, made by dark energy, gets stronger than the gravity it contains and tears everything apart (even atoms). Recently, the inflation started accelerating, probably because the farther objects are from each other, the smaller effect gravity has on them because gravity gets less at the square of the distance. If the acceleration caused by dark energy increases without limit, with the dark energy eventually becoming so strong that it completely overwhelms the effects of the gravitational, electromagnetic and weak nuclear forces, the universe will rip itself apart, and everything will stop.The Big Crunch is the least likely possibility of the death of the Universe. It is practically proven inaccurate. If gravity overcomes dark energy, the universe could ‘shrink’, decrease or decay, and basically reverse the Big Bang to destroy the Universe. Everything would collide. Interestingly, some predictions say that once the universe is very close to a singularity again, the warping of space-time will be so chaotic and so violent that space and time will actually “shatter” into “droplets” and all current concepts of time, distance and direction will become meaningless. There is also a small possibility that it will bounce and create a new Big Bang. Another possibility is that quantum fluctuations, the temporary change in the amount of energy in a point in space, could start a new Big Bang, which would spread through our universe. This is very, very unlikely.If the geometry of space is open, there are different ends in sight. A negatively curved universe would expand forever without dark energy, so dark energy accelerates it. We really don’t know enough about dark energy to understand the implications of this. A lot of the outcome would depend on the relationship between dark energy and gravity. One outcome scientists are theorizing is the Big Freeze, which is similar to the Big Rip, but more likely to happen. Essentially, entropy, the moving from order to disorder, will increase until it reaches a maximum value. Energy in the system will be diffused completely equally, which means there is no more energy to be used anywhere, and mechanical motion within the Universe will desist. The Universe would end with “heat death”. It would become so huge that stores of gas would be dispersed so thin that there wouldn’t be enough anywhere for stars to form. If this happened, time would be an “endless void” in which nothing could happen because matter and energy are too spread out to interact. All that would remain are black holes. While thinking about this, don’t worry. Our star will explode before any of this happens (hopefully), and our civilization will end even sooner. I’m Julia Margie, and that was “A Short Biography of Our Universe.