The 90's were fundamental years for the study of the expansion of the Universe, many great Astronomers and Physicists around the world were working on the explanation of the evolution of the Universe since it has been one of the main questions of humanity since the very first stages of history. But there are many remarks to be made in this topic. First, the discovery of its acceleration is quite recent and it has changed many of the models of Cosmology; measuring light from very faint objects in space is really hard so the experimental evidence of this models was not possible in Einstein's times.
In 1929 Edwin Hubble measured the expansion of the Universe, one of the most important discoveries in the history of Astronomy and Physics because it made us see in more concrete terms what we could mean by the fate of the Universe. This discovery made scientists formulate many theories and models that would give a fair explanation to what was observed.
With the expansion of the Universe as an anchor, theory converged on a standard model of the Universe, which was still in place in 1998, the theory was basically a decelerating model of the Universe given by the gravitational attraction of the massive bodies that would eventually stop the expansion and make the Universe contract.
Einstein himself tried to explain the observed expansion of the Universe implying that there must be something that halts the quick gravitational contraction that one usually expects, he didn't like the idea of an expanding Universe. With the cosmological constant Einstein attempted to balance the gravitational attraction with the negative pressure associated with an energy density inherent to the vacuum. His studies were also backed up by some scientists who made the mathematical formulation of this last theory.
The nobel winners Saul Perlmutter, Adam Riess and Brian Schmidt (2011) were the ones that made the great discovery of the acceleration of this expansion, but how did they do it?
A really smart way to measure distances and red shifts from distant objects is by observing Supernovae, you can take the brightness of a supernova as an indicator of how far away it is. The fainter it is, the further away it is from us, and how red it gets tells you how much the Universe has stretched since the supernova exploded, because while the light is traveling to us, its wavelength stretches by the exact same proportion as the Universe stretches. So, this is a very direct way of plotting how much the Universe has stretched as a function of time. Also, the brightness of supernovae is so big that they can be observed even if they are really far from us, even around distances of 6 billion light years.
But only Type Ia is usefull for this manner because they all have the same brightness when they explode, and it was only in the mid-1980s that this subclass of Supernovae was identified, so we see that this studies could not have been in Einstein's time. The interesting result in these observations is that the most distant supernovae are fainter than everyone expected, and that could only be explained by an accelerating Universe.
In the late 90's, at the time when the discovery of the accelerating Universe was made, the standard model was based on the theory of general relativity, and two assumptions. Assumption one was that the Universe is homogenous and isotropic on large scales, and assumption two that it is composed of normal matter, i.e. matter whose density falls directly in proportion to the volume of space, which it occupies. But the discovery of these nobel winners made us re formulate our understanding of the composition of the Universe and its composition in the early times after the Big Bang.
Apparently we have a Universe that is dominated by some new ingredient, some previously unknown “Dark Energy” that makes the Universe expand faster and faster. Recent estimations say that in the composition of the Universe today is 70% dark energy, 25% is dark matter and only 5%is the baryonic matter that is what we are more concerned about.
The most accepted model suggests that early after the Big Bang, the acceleration of the universe was null, but when matter started diluting by the explasion, dark energy became dominant and expansion started accelerating. Recent observations are focused on faint objects that will give us more information about the rate at which the acceleration is correct and it has become one of the main problems of modern cosmologists because we don't know much about dark energy and it could take our understanding of the Universe to a whole new level.
In 1929 Edwin Hubble measured the expansion of the Universe, one of the most important discoveries in the history of Astronomy and Physics because it made us see in more concrete terms what we could mean by the fate of the Universe. This discovery made scientists formulate many theories and models that would give a fair explanation to what was observed.
With the expansion of the Universe as an anchor, theory converged on a standard model of the Universe, which was still in place in 1998, the theory was basically a decelerating model of the Universe given by the gravitational attraction of the massive bodies that would eventually stop the expansion and make the Universe contract.
Einstein himself tried to explain the observed expansion of the Universe implying that there must be something that halts the quick gravitational contraction that one usually expects, he didn't like the idea of an expanding Universe. With the cosmological constant Einstein attempted to balance the gravitational attraction with the negative pressure associated with an energy density inherent to the vacuum. His studies were also backed up by some scientists who made the mathematical formulation of this last theory.
The nobel winners Saul Perlmutter, Adam Riess and Brian Schmidt (2011) were the ones that made the great discovery of the acceleration of this expansion, but how did they do it?
A really smart way to measure distances and red shifts from distant objects is by observing Supernovae, you can take the brightness of a supernova as an indicator of how far away it is. The fainter it is, the further away it is from us, and how red it gets tells you how much the Universe has stretched since the supernova exploded, because while the light is traveling to us, its wavelength stretches by the exact same proportion as the Universe stretches. So, this is a very direct way of plotting how much the Universe has stretched as a function of time. Also, the brightness of supernovae is so big that they can be observed even if they are really far from us, even around distances of 6 billion light years.
But only Type Ia is usefull for this manner because they all have the same brightness when they explode, and it was only in the mid-1980s that this subclass of Supernovae was identified, so we see that this studies could not have been in Einstein's time. The interesting result in these observations is that the most distant supernovae are fainter than everyone expected, and that could only be explained by an accelerating Universe.
In the late 90's, at the time when the discovery of the accelerating Universe was made, the standard model was based on the theory of general relativity, and two assumptions. Assumption one was that the Universe is homogenous and isotropic on large scales, and assumption two that it is composed of normal matter, i.e. matter whose density falls directly in proportion to the volume of space, which it occupies. But the discovery of these nobel winners made us re formulate our understanding of the composition of the Universe and its composition in the early times after the Big Bang.
Apparently we have a Universe that is dominated by some new ingredient, some previously unknown “Dark Energy” that makes the Universe expand faster and faster. Recent estimations say that in the composition of the Universe today is 70% dark energy, 25% is dark matter and only 5%is the baryonic matter that is what we are more concerned about.
The most accepted model suggests that early after the Big Bang, the acceleration of the universe was null, but when matter started diluting by the explasion, dark energy became dominant and expansion started accelerating. Recent observations are focused on faint objects that will give us more information about the rate at which the acceleration is correct and it has become one of the main problems of modern cosmologists because we don't know much about dark energy and it could take our understanding of the Universe to a whole new level.
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