The invisible strings of expansion

In early years, people believed that the universe was expanding more slowly than it used to and that the galaxies at the edge of the universe were slowing down.

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But after careful observations and calculations like the Supernova Cosmological project, it was found that universe is nowhere near slowing down and it is actually accelerating. The galaxies that are at the edge of cosmos are in fact moving faster and away from us. Astonished astronomers didn't know how to explain this phenomenon however they did come up with a few possible explanations.

It was suggested that it was either a result of queer energy fluid-like material in space or in the field that created this acceleration. Extended researches in gravitational lensing, cosmic microwave background also suggests that the universe is not just empty.

The Cosmological constant, which is the measure of the energy density of vacuum of space, after analysing the red shift of distant galaxies, suggest that universe is indeed accelerating. This constant was introduced by Albert Einstein in 1917. The rate at which the celestial bodies move away from earth is measured by red shift.

Red shift : When a luminous body emitting electromagnetic spectrum moves away from us, the electromagnetic waves have to travel a larger distance to reach us. It gets stretched out and shifts to larger wavelength in order to cover a larger distance.

The gravity works to collapse the universe whereas the cosmological constant works to expand it. If both equal each other in magnitude, the universe would be static with no expansion or contraction rate. On the basis of various observations universe is still expanding and it is not slowing down.

The question that still nags us is that, where did repulsive gravity force come from?

Research suggests that this might have been a fragment of Universe's early inflation.

The theory of cosmological inflation suggests that the expansion of the universe was very much a result of something like Einstein cosmological constant which works up to expand space-time. It was called the Vacuum energy, a background lowest state of cosmological energy, produced as a result of inflation.

This exponential inflation epoch lasted up to 10^-36 seconds before singularity and 10^-33 seconds after big bang singularity. It was put forward by Alan Guth in 1979. Transferring information from photon to photon can take more than ages of multi-universes due to their disconnection and territorial alignment out of others horizons. But the theory suggests all photons have almost the same temperature, which implies that they should have been in contact with each other before starting of the early universe.

The universe had an exponential expansion by 10^26 of a factor when all of the matter was almost in contact with each other. This inflation gave birth to the energy from steady acceleration of space, to which we call the Dark energy.

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This hypothetical form of energy, an anti-gravitational force, acts in opposite direction of gravity, that is pushing the matter away from each other. The universe's acceleration and expansion are viable due to this particular force. It makes up almost 72% of the universe and 68.3% of total energy is contributed by dark energy. It cannot be observed directly, but rather by gravitational interactions between celestial objects.

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The density of dark energy is lesser than that of the ordinary matter but in terms of mass and energy, it usurps the top position due to its uniformity across space. It doesn't react with any of the four fundamental forces of nature except gravity. It is thought to be quintessence or the fifth fundamental force of nature or the fifth element. Being a scalar field, it only has magnitude and no direction. A hypothetical particle can carry this particular energy, called the Chameleon particle's, it's mass varies with respect to surroundings.

Einstein made a statement that, " space is not empty and that it posses its own energy. It will not weaken or diminish with the expansion of space as it is its intrinsic property."

Since Einstein's theory of Mass Energy equivalence, E= mc^2 suggests that mass and energy are interchangeable. It was suggested that the empty space was actually made up of a huge number of virtual particles that appear and disappear. But this theory was disproved, as the energy that these particles would give to space was higher by 10^120 to the original calculated quantity.

In simple words, the dark energy can be related to the hot air balloon that expands the universe, the gravity and Dark matter as an anchor weighing it down. After an extensive voyage through physics, the Dark energy remains still a mystery and to this date, this particular division of physics has a number of unexplored branches than any other.