It is now well established through observations that the universe is expanding which has been speeding up over time. However, the cause of the expansion is not yet known. It is assumed to be a mysterious energy acting opposite to gravity causing this expansion.
This energy is termed as “dark energy” and it is estimated that it makes up to 72 percent of the constituents in the universe. A new experiment has confirmed that it is not a new force. The study appears in the Physical Review Letters journal. Ed Copeland, a physicist from the University of Nottingham said that the experiment related to cosmology and atomic physics helped in ruling out several models which have been proposed for the explanation of dark energy and will eliminate many more models.
These anomalies have helped in putting constraints on the fifth force and helped in constructing alternatives to general relativity for explaining the increasing rate of expansion of the Universe. Some of the alternatives are chameleon theory and symmetron theory.
If another force present in the Universe was responsible for almost 75 percent of its mass-energy density then it should be easy to detect. But if it acts opposite to gravity i.e. a repulsive force then it should be weakest in the area where gravity is the strongest force. This should hold true for objects with significant mass such as a planet.
An experiment was designed to observe this anti-gravitational force. Within a sealed vacuum chamber, a large aluminium sphere and small weights – atoms of rubidium-87 were placed and atom interferometry was used for measuring the acceleration of the smaller weight towards the larger one. If a fifth force was present then the atom should have been veered off its path as it moved towards the sphere. But no such deviation was observed which clearly explains that no such anti-gravity force was present in the chamber. It does not mean that there is no fifth force at all. However, the force can be defined by several constraints which also means that similar constraints can be placed on chameleon and symmetron theories.
There may not be always a straightforward answer to fundamental questions of this nature so the correct questions are asked to narrow down on the correct answer. Answering this question would give significant answers about the evolution of the universe.
February 5, 2019(updated May 27, 2019) Published by Kshitij Kumar
Dark Matter & the Ultimate Fate of the Universe
So what is dark energy?
Well, the easy answer is that we do not recognize.
It looks to contradict several of our understandings regarding the manner the universe works. We all recognize that light-weight waves, conjointly known as radiation, carry energy. You feel that energy the instant you step outside on a hot summer day.
More is unknown than is thought. we all know what quantity dark energy there’s as a result of we all know however it affects the universe’s enlargement. apart from that, it’s an entire mystery. however, it’s a very important mystery. It seems that roughly sixty-eight of the universe is dark energy. matter makes up concerning twenty-seventh. the remainder – everything on Earth, everything ever determined with all of our instruments, all traditional matter – adds up to but five-hitter of the universe. come back to think about it, perhaps it should not be referred to as “normal” matter the least bit since it’s such a tiny low fraction of the universe.
One clarification for dark energy is that it’s a property of area. the physicist was the primary person to understand that a vacant area isn’t anything. the area has superb properties, several of that are simply starting to be understood. the primary property that Einstein discovered is that it’s potential for extra space to come back into existence.
Then one version of Einstein’s gravity theory, the version that contains a constant, makes a second prediction: “empty space” will possess its own energy. as a result of this energy may be a property of the area itself, it’d not be diluted as area expands. As extra space comes into existence, a lot of this energy-of-space would seem. As a result, this way of energy would cause the universe to expand quicker and quicker. sadly, nobody understands why the constant ought to even be there, abundant less why it’d have precisely the right worth to cause the discovered acceleration of the universe.
Another rationalization for the way house acquires energy comes from the scientific theory of matter. during this theory, “empty space” is really choked with temporary (“virtual”) particles that regularly type and so disappear. however once physicists tried to calculate what quantity energy this is able to offer empty house, the solution came out wrong – wrong by a great deal. the amount came out 10120 times too massive. that is a one with a hundred and twenty zeros once it. It’s laborious to urge a solution that unhealthy. that the mystery continues.
Another rationalization for dark energy is that it’s a brand new quite high-octane energy fluid or field, one thing that fills all of the areas however one thing whose result on the enlargement of the universe is that the opposite of that of matter and traditional energy. Some theorists have named this “quintessence,” when the fifth part of the Greek philosophers. But, if quintessence is that the answer, we have a tendency to still do not know what it’s like, what it interacts with, or why it exists. that the mystery continues.
The last chance is that Einstein’s theory of gravity isn’t correct. that will not solely have an effect on the enlargement of the universe, however, it might additionally have an effect on the method that ordinary matter in galaxies and clusters of galaxies behaved. This truth would supply the way to make your mind up if the answer to the dark energy downside may be a new gravity theory or not: we have a tendency to might observe however galaxies close in clusters. however, if it will prove that a brand new theory of gravity is required, what quite a theory would it not be? however, might it properly describe the motion of the bodies within the system, as Einstein’s theory is thought to try toto, and still provide the U.S.A. with the various prediction for the universe that we have a tendency to need? There area unit candidate theories, however none area uncompelling. that the mystery continues.
The issue that’s required to make your mind up between dark energy potentialities – a property of area, a brand new dynamic fluid, or a brand new theory of gravity – is additional knowledge, higher knowledge.
Dark energy or dark matter?
Dark energy makes up most of the universe, however, substance additionally covers a sizeable chunk. Comprising nearly twenty-seven p.c of the universe, and eighty p.c of the matter, substance additionally plays a dominant role.
Like dark energy, substance continues to confound scientists. whereas dark energy could be a force that accounts for the increasing universe, substance explains, however, teams of objects operate along.
In the Fifties, scientists learning different galaxies expected gravity to cause the centres to rotate quicker than the outer edges, supported the distribution of the objects within them. To their surprise, each region revolved at a similar rate, indicating that the spiral galaxies contained considerably a lot of mass than they perceived to. Studies of gas within elliptical galaxies and of clusters of galaxies disclosed that this hidden matter was unfolded throughout the universe. Scientists have a variety of potential candidates for substance, move to unbelievably dim objects to strange particles. however, regardless of the supply of each substance and dark energy, it’s clear that the universe is stricken by things that scientists cannotconventionally observe.
The fate of the Universe
The evolution of the universe is ruled by the number of matter and dark energy it contains, however, the densities of matter and dark energy—their concentrations inside given volume of space—are affected terribly otherwise by cosmic growth. we have a decent plan of what quantity matter the universe holds, and though we do not understand exactly what it’s, we have a tendency to do comprehend it is plagued by gravity. The key, then, to understanding the ultimate fate of the Universe lies in understanding the opposite half this dark equation: dark energy.
Currently, cosmologists perceive nearly nothing regarding dark energy albeit it seems to comprise regarding seventy % of the mass-energy content of the universe. they’re urgently seeking to uncover its elementary properties: its strength, its permanency, and any variation with direction. they need to learn the properties of matter before they will verify its influence on the increasing Universe.
This evolution in cosmic scale is schematically shown within the higher than the figure for many cosmologies. during a universe with a high density of matter, the Edwin Bubble growth that began with the large Bang continues to decelerate thanks to the gravitation attraction of the matter filling the universe, ending during a massive crunch. during a universe with a lower vital density of matter, the growth coasts. during a universe with dark energy additionally as matter, the initial slowing is reversed at late times by the increasing dominance of dark energy.
If the hypothetic dark energy continues to dominate the universe’s energy balance, then the present growth of house can still accelerate, exponentially. Structures that don’t seem to be already gravitationally certain can ultimately fly apart. the planet and therefore the Milky Way Galaxy would stay undisturbed whereas the remainder of the universe seems to run far from the USA. The nature of dark energy is presently a matter of speculation. Some believe that dark energy could be “vacuum energy,” diagrammatic by the “cosmological constant” (Λ, the Greek capital letter lambda) normally relativity theory, a relentless uniform density of dark energy throughout all of the house that’s freelance of your time or the universe’s growth. This notion was introduced by Einstein and is according to our restricted observations so far. instead, dark energy would possibly vary with time. solely new sorts of observations will settle the difficulty.
We do understand this: Since the area is everyplace, this dark energy force is everyplace, and its effects increase as area expands. In distinction, gravity’s force is stronger once things area unit close and weaker after they area unit so much apart. as a result of gravity is weakening with the enlargement of area, dark energy currently makes up over 2/3 of all the energy within the universe. It sounds rather strange that we’ve got no firm plan regarding what makes up seventy-four of the universe. It’s as if we have a tendency to had explored all the land on the world Earth associate degreed ne’er all told our travels encountered an ocean. however currently that we’ve caught sight of the waves, we wish to grasp what this immense, strange, powerful entity extremely is.
The strangeness of dark energy is thrilling.
It shows scientists that there’s a spot in our information that must be crammed, beckoning the manner toward associate degree undiscovered realm of physics. we’ve got before the United States the proof that the cosmos could also be organized immensely otherwise than we have a tendency to imagine. Dark energy each signals that we have a tendency to still have a good deal to find out, and shows the United States that we have a tendency to stand poised for an additional nice leap in our understanding of the universe.
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