The Universe
Light and the Formation of the Universe

Critical Density
The “critical density” is the average density of matter required for the Universe to just halt its expansion, but only after an infinite time. A Universe with the critical density is said to be flat. In his theory of general relativity, Einstein demonstrated that the gravitational effect of matter is to curve the surrounding space. In a Universe full of matter, both its overall geometry and its fate are controlled by the density of the matter within it (Swinburne University, 2013).
The critical density for the Universe is approximately 10-26 kg/m3 (or 10 hydrogen matters per cubic meter) and is given by: H is the Hubble constant and G is Newton’s gravitational constant.
Attempts to measure the actual density of the Universe have basically followed one of two methods (Swinburne University, 2013).
Gravity and Light
Gravity is nothing more than an effect of the curvature of spacetime. This curved is caused by the presence of matter, any matter. But you need a great deal of matter to cause even a small curve.
Light is a form of energy, so is mass E=MC^2 meaning that mass equals a massive amount of energy, It takes mass of the entire Earth to cause even a small curve, A beam of light contains nearly infinitely less energy and therefore causes barely any curve.
Light is a “massless” particle but) that only means it has no “rest mass”. Anything equivalent to mass energy, pressure, even angular momentum-can bend spacetime. All part of what is called the stress energy lensor in general relativity.
Gravity is a force that attracts mass. Light is a wave, a wave does not have mass, only frequency, amplitude, and speed. The particles it vibrates have mass which are affected by gravity, in turn bending the wave. Since gravity is strong enough to bend light, then light cannot be stronger then gravity so that it could affect back.
The photon does not have mass and cannot affect gravity. The bending is due to the topography of spacetime deforming to the presence of matter where light travels in a “straight” line its plane of reference (Bennett, 2012).
Gravitational Lensing
Because mass distort the space around them, massive objects can therefore act as gravitational lenses that bend light beams passing nearby. Because the light bending angle of a gravitational lens depends on the masses of an object can be measured by observing how strongly they distort light paths. light and the formation of the Universe
Curvature of Space
Einstein’s general theory of relativity describes gravity in terms of the geometry of both spaced time. Space is flat and clocks tick normal. Closer to a source of gravity, however, clocks slow down and space is curved. Measuring the curve is very difficult.
According to relativity theory, the strong gravity of a massive object such as the Sun produces curvature in nearby space which allows the path of light or radiowaves passing near the object.
Curvature of space is defined as a change in geometry of space that is produced in the vicinity of a massive object and is responsible for the force we call gravity. The overall geometry of the Universe, may also be carved, depending on its overall mass energy content (Bennett, 2012).
Cosmic Microwave Background Radiation (CMBR)
According to the theories of physics, if we were to look at the Universe one second after the Big Bang, what we would see is a 10-billion degree sea of neutrons, protons, electrons, anti-electrons positrons, photons, and neutrinos. As time went on, we would see the Universe cool, the neutrons either decaying into protons and electrons, or combining with protons to make deuterium (an isotope of hydrogen). As it continued to cool, it would eventually reach the temperature where electrons combined with nuclei to form neutral atoms. Before this "recombination" occurred, the Universe would have been opaque because the free electrons would have caused light