Using Cepheid Variables to Measure Distance
The Size and Expansion of the Universe How do we know how big the Universe is? And how old it is? How do we know it is expanding? What evidence is there for the Big Bang? What will happen to the Universe? Does this point to God’s creation? Notes from the Spacebook website of Las Cumbres Observatory Parallax is the first way to find out how far away things are. You can see parallax by holding your thumb out at arm’s length, and closing one eye and then another.
Measurements of parallax work out to about 1000 parsecs (1 parsec is about 3.26 light years).
Using Cepheid Variables to Measure Distance Cepheid variable stars are intrinsic variables which pulsate in a predictable way. In addition, a Cepheid star's period (how often it pulsates) is directly related to its luminosity or brightness.
1
Cepheid variables are extremely luminous and very distant ones can be observed and measured. Once the period of a distant Cepheid has been measured, its luminosity can be determined from the known behavior of Cepheid variables. Then its absolute magnitude and apparent magnitude can be related by the “distance modulus equation”, and its distance can be determined. Cepheid variables can be used to measure distances from about 1kpc to 50 Mpc (about 150 million light years). [So from this we know the Universe is at least millions of years old. Even if we were not convinced by Cepheid variables, we could simply look at a galaxy that is very far away and deduce that it is millions of light years away by how small it looks at its distance. We can see this effect even more with today’s telescopes, where we can resolve distant galaxies into their myriad stars. The Andromeda galaxy is roughly 2.4 million light years away. If the Universe were 6,000 years old, light from this galaxy would have only propagated 1/400 of the way towards Earth, and we would not see it at all.]
Using Type 1A Supernovae to Measure Distance Type 1a supernovae are all caused by exploding white dwarfs which have companion stars. The gravitational pull of the white dwarf causes it to take matter from its companion star. Eventually it reaches a high enough mass (about 1.44 solar masses) that it cannot support itself against gravitational collapse and explodes. [Some type 1a supernovae are caused by two white dwarf stars combining.] All type 1a supernovae reach nearly the same brightness at the peak of their outburst with an absolute magnitude of -19.3±0.03. They then follow a distinct curve as they decrease in brightness. So when astronomers observe a type 1a supernova, they can measure its apparent magnitude, knowing what its absolute magnitude is. They can then use the distance modulus equation to calculate the distance to the supernova, and the galaxy that it is in. Type 1a supernovae can be used to measure distances from about 1 Mpc to over 1000 Mpc (over 3 billion light years). [Actually astronomers are able to do this past 10 billion light years now.] 2
So we can measure the distances of objects out to huge distances. And what we find is that the further away things are, the faster they are moving away from us.
How do we figure out how they are moving, towards or away from us?
(from University of Nebraska-Lincoln website)
(Spectra of stars, from University of Nebraska-Lincoln website)
3
The Doppler Effect (from Cornell University website)
The Expansion of the Universe Edwin Hubble discovered that the universe is expanding when he found that the further away a galaxy was, the more its spectral lines were redshifted. So nearby galaxies are moving away from us slowly, and far away galaxies are moving away much more quickly. Their apparent motion isn’t due to their motion through space, but the expansion of space itself. Graph from: http://www.google.com/imgres?imgurl=http://www.uni.edu/morgans/astro/course/Notes/ section3/hubblelaw.gif&imgrefurl=http://www.uni.edu/morgans/astro/course/Notes/sectio n3/new13.html&h=301&w=421&sz=5&tbnid=5JEigeUUXPd8M:&tbnh=82&tbnw=115&prev=/search%3Fq%3Dgalaxy%2Bdistance%2Bversus%2Bs peed%26tbm%3Disch%26tbo%3Du&zoom=1&q=galaxy+distance+versus+speed&usg= __TPMgTi0KUd_HUHYfwET538G71c4=&sa=X&ei=wdF4UNP_OZO89QS4vIAQ&ved= 0CCgQ9QEwBA A Hubble Diagram, simply a plot of galaxy velocity versus galaxy distance (using supernovae).
4
The expanding universe can be compared to what happens when a loaf of bread with raisins in it bakes and expands in an oven. As the bread rises and expands, the raisins seem to move away from each other. They are not moving within the dough, but as the dough expands, the distance between them becomes greater. In this scenario, a raisin on one edge of the bread would see raisins on the opposite side of the bread moving away with a greater speed than nearby raisins. Or (from Edward Lu website) you can look at it as an expanding lattice (a print by Escher):
As far as the eye can see, the grid goes on forever. Now imagine each of the sticks between nodes all getting longer. The nodes separate, and this Escher universe expands. But it isn’t expanding into anything, it is just getting larger. That’s exactly the same as what we notice about our own universe. All the galaxies appear to be moving away from each other. But there is no edge to the universe, and therefore there also isn’t a center to the universe (which is also the reason the Big Bang didn’t happen at a point). At least we haven’t seen an edge yet.
We mainly believe there is no edge or center because there is no evidence of a central place. From any vantage point, everything looks like it is moving away.
From Wikipedia (big bang):
The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe.[1] According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state. According to the most recent measurements 5
and observations, the Big Bang occurred approximately 13.75 billion years ago, [2][3] which is thus considered the age of the Universe.[4][5] After its initial expansion from a singularity, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. While protons and neutrons combined to form the first atomic nuclei only a few minutes after the Big Bang, it would take thousands of years for electrons to combine with them and create electrically neutral atoms. The first element produced was hydrogen, along with traces of helium and lithium. Giant clouds of these primordial elements would coalesce through gravity to form stars and galaxies, and the heavier elements would be synthesized either within stars or during supernovae. The Big Bang is a well-tested scientific theory and is widely accepted within the scientific community. It offers a comprehensive explanation for a broad range of observed phenomena. Since its conception, abundant evidence has been uncovered in support of the model. [6] The core ideas of the Big Bang—the expansion, the early hot state, the formation of helium, and the formation of galaxies—are derived from many observations that are independent from any cosmological model; these include the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram for Type Ia supernovae. [All these things match what is expected for a Universe that came from the Big Bang.] As the distance between galaxy clusters is increasing today, it can be inferred that everything was closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,[7][8][9] and large particle accelerators have been built to experiment in such conditions, resulting in further development of the model. On the other hand, these accelerators have limited capabilities to probe into such high energy regimes. There is little evidence regarding the absolute earliest instant of the expansion. Thus, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on. Georges Lemaître first proposed what would become the Big Bang theory in what he called his "hypothesis of the primeval atom." Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions such as homogeneity and isotropy of space. The governing equations had been formulated by Alexander Friedmann. In 1929, Edwin Hubble discovered that the distances to far away galaxies were generally proportional to their redshifts— an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity. [10] While the scientific community was once divided between supporters of the Big Bang and those of alternative cosmological models, most scientists became convinced that some version of the Big Bang scenario best fit observations after the discovery of the cosmic microwave background radiation in 1964, and especially when its spectrum (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a black body. Since then, astrophysicists have formulated further hypotheses to account for some discrepancies that have arisen within the model. 6
The cosmic background radiation is a strong confirmation. It was predicted to be a result of the Big Bang, the radiation released at about 380,000 years after the Big Bang, when the universe thinned sufficiently so that the photons could travel without being absorbed. It was at just the right temperature as expected, when its spectrum was adjusted for the long distance away. Its texture is correct for the kinds of variations that led to the formation of galaxies.
(from NASA website) Will the Universe expand forever or collapse on itself? Initially, two teams of scientists (1998) discovered from observing Type 1a supernovae, that the universe appeared to be expanding at an increasing rate. Rather than a linear increase (with distance) in expansion as expected, or a reduced expansion in recent times due to gravity slowing the expansion down, the more recent (closer) objects are moving away faster than they should be, indicating that the expansion is speeding up. The evidence was somewhat sparse, with not very many supernovae observed. More evidence has occurred in more recent years:
Sloan survey shows dark energy who's boss Based on new, more accurate measurements of distant galaxies, astronomers believe the expansion of the universe started accelerating some 5 to 7 billion years ago. By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts — Published: March 30, 2012
7
The record of baryon acoustic oscillations (white circles) in galaxy maps helps astronomers retrace the history of the expanding universe. These schematic images show the universe at three different times. The representative-color image on the right shows the "cosmic microwave background," a record of what the young universe looked like 13.7 billion years ago. The small density variations present then have grown into the clusters, walls, and filaments of galaxies that we see today. These variations included the signal of the original baryon acoustic oscillations (white circle, right). As the universe has expanded (middle and left), evidence of the baryon oscillations has remained, visible in a "peak separation" between galaxies (the larger white circles). The SDSS-III results announced today (middle) are for galaxies 5.5 billion light-years distant, at the time when dark energy turned on. Comparing them with previous results from galaxies 3.8 billion light-years away (left) measures how the universe has expanded with time. Credit: E.M. Huff/the SDSS-III team/South Pole Telescope team. Graphic by Zosia Rostomian
[Distances between galaxies is larger than it would be if the expansion were not accelerating.] Astronomers have made the most accurate measurement yet of galaxy distances in the faraway universe, giving an unprecedented look at the time when dark energy turned on. Some 5 to 7 billion years ago, the expansion of the universe stopped slowing due to gravity and started to accelerate due to dark energy. Yet the nature of dark energy remains a puzzle that astronomers are seeking to solve. The new measurement came from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the third Sloan Digital Sky Survey (SDSS-III). "We see the influence of dark energy on cosmic structure, but we have no idea what it is. The data gathered by this survey will help answer that question," said Daniel Eisenstein from the HarvardSmithsonian Center for Astrophysics in Cambridge, Massachusetts. "There's been a lot of talk about using galaxy maps to find out what's causing accelerating expansion," said David Schlegel from the U.S. Department of Energy's Lawrence Berkeley National Laboratory in California, BOSS's principal investigator. "We've been making a map, and now we're using it — starting to push our knowledge out to the distances when dark energy turned on." Investigating Dark Energy One of the most amazing discoveries of the last two decades in astronomy, recognized with the 2011 Nobel Prize in physics, was that not only is our universe expanding, but it also is accelerating. Galaxies are becoming farther apart from each other faster and faster with time. The leading contender for the cause of the accelerating expansion is a postulated new property of space dubbed "dark energy." Alternatively, the universe may be accelerating because gravity deviates from Einstein's general theory of relativity and becomes repulsive at very large distances. Whether the answer to the puzzle of the accelerating universe is dark energy or modified gravity, the first step to finding that answer is to measure accurate distances to as many galaxies as possible. From those measurements, astronomers can trace out the history of the universe's expansion. BOSS is producing the most detailed map of the universe ever made by using a new custom-designed spectrograph of the SDSS 2.5-meter telescope at Apache Point Observatory in New Mexico to observe more than a million galaxies over six years.
8
The astronomers' announcement is based on a map of more than 250,000 galaxies created from the first year and a half of BOSS observations. Some of these galaxies are so distant that their light has traveled more than 6 billion years to reach Earth — nearly half the age of the universe. Surveying the Cosmos Maps of the universe like BOSS's show that galaxies and clusters of galaxies are clumped together into walls and filaments, with giant voids between. These structures grew out of subtle variations in density in the early universe, which bore the imprint of "baryon acoustic oscillations" — pressure-driven acoustic (sound) waves that passed through the early universe. [Baryons are particles made up of three quarks. The most familiar baryons are protons and neutrons.] Billions of years later, the record of these sound waves can still be read in our universe. "Because of the regularity of the ancient sound waves, there's a slightly increased probability that any two galaxies today will be separated by about 500 million light-years, rather than 400 million or 600 million," said Eisenstein. In a graph of the number of galaxy pairs by separation distance, that magic number of 500 million lightyears shows up as a peak, so astronomers often speak of the "peak separation." The position of this peak depends on the amount of dark energy in the universe. But measuring the distance between galaxies depends critically on having the right distances to the galaxies in the first place. That's where BOSS comes in. "We've detected the peak separation more clearly than ever before," said Nikhil Padmanabhan of Yale University. "These measurements allow us to determine the contents of the universe with unprecedented accuracy."
Cosmic acceleration, further evidence
"Cosmic mirages" confirm accelerated cosmic expansion These results independently indicate that the expansion of the universe is accelerating, which suggests that the universe must be filled with a mysterious energy component called dark energy. By University of Tokyo, Kashiwa, Japan — Published: April 11, 2012
9
Image of SDSSJ12260006, a new gravitationally lensed quasar discovered in this survey. The quasar image in the original image of the Sloan Digital Sky Survey, which has been used for the actual survey to identify gravitational lensing, looks only slightly extended, but the Hubble Space Telescope image clearly exhibits two distinct quasar images (white) as well as a massive galaxy in between the quasar images (orange) that produces gravitational lensing.
Quasars are luminous objects powered by accretion of gas into supermassive black holes at the centers of distant galaxies. A quasar is typically located far away. Gravitational lensing is a phenomenon in which a distant object is split into two or more images due to the gravity of a massive foreground object. The phenomenon of gravitational lensing, often called a “cosmic mirage”, was first discovered in 1979, and since then more than 100 gravitationally lensed quasars have been reported. An international team of researchers led by Masamune Oguri and Naohisa Inada from the Nara National College of Technology in Japan conducted a large survey to search for gravitationally lensed quasars in the massive data sets of the Sloan Digital Sky Survey (SDSS). During almost 10 years of careful examinations of 100,000 quasars, the team successfully discovered nearly 50 new gravitationally lensed quasars in total, significantly increasing a sample of cosmic mirages. The frequency of gravitational lensing, which can be measured by counting the number of gravitationally lensed quasars within a given quasar catalog, allows one to infer the expansion speed of the universe because the accelerated expansion increases the distance to each quasar and, therefore, enhances the chance of gravitational lensing. The team measured the probability of gravitational lensing among distant quasars to be about 0.05 percent, which was then compared with detailed theoretical calculations to extract information on the expansion history. The result indicates that the expansion of the universe is indeed accelerating, which suggests that the universe must be filled with a mysterious energy component called dark energy.
10
Illustration of the gravitational lensing measurement of the cosmic expansion speed. The accelerated expansion increases the distance to the quasar, giving rise to higher chance of having a massive galaxy close to the light path to produce gravitational lensing. Credit: Kavli IPMU
“The accelerated cosmic expansion is one of the central problems in modern cosmology,” Oguri said. “In 2011, the Nobel Prize in physics was awarded to the discovery of the accelerated expansion of the universe using observations of distant supernovae. A caution is that this method using supernovae is built on several assumptions, and therefore independent checks of the result are important in order to draw any robust conclusion. Our new result using gravitational lensing not only provides additional strong evidence for the accelerated cosmic expansion, but also is useful for accurate measurements of the expansion speed, which is essential for investigating the nature of dark energy.” Careful comparisons with other cosmological observations led to the conclusion that dark energy behaves almost like Einstein’s cosmological constant. [Einstein and others believed that the Universe must be static. He inserted a “cosmological constant” in his equations to make this happen. Many scientists initially rejected the Big Bang theory because it implies the Universe had a beginning. The evidence eventually became overwhelming.] “Statistical methods on gravitationally lensed quasars have been known to be sensitive to the expansion history of the universe,” Masashi Chiba from Tohoku University said, “therefore actively studied by Japanese researchers in the 1990s. Observations of gravitational lensing at that time already hinted at the presence of dark energy, but both due to the small sample size and large uncertainty in the theoretical modeling of lensing rates, the result was not widely accepted. This research conducted an enormous survey of gravitationally lensed quasars and adopted much more sophisticated theoretical calculations to build a very convincing case for the accelerated cosmic expansion.” “Studies of dark energy — cosmological constant — were popular in Japan already in the early 1990s, largely because of pioneering work by Fukugita,” said Yasushi Suto from the University of Tokyo. “This survey of gravitationally lensed quasars was initiated and organized by Oguri and Inada, who were graduate students when the survey started, within the large international SDSS collaboration, and they led the team to success. This result is important in that it confirms the presence of dark energy independently from the observation of supernovae.”
11
Detailed properties of dark energy are planned to be explored in the SuMIRe project, an international survey project led by Kavli IPMU using the Subaru Telescope. “This result demonstrates that Japanese theoretical and observational cosmologists will play an essential role in the SuMIRe project,” Suto said. “This result creates big momentum for the survey of the cosmic dark energy by the SuMIRe project,” Chiba said. [So we have looked at three methods which all indicate that the Universe’s expansion rate is increasing.] ---------------------------------------------------------------------------------
The Universe is much larger than 13.7 billion light years across, one reason being that the objects that emitted light that reached us 13.7 billion years later are now much farther away. But the Universe could be much bigger than that, in fact it could be infinite, or a huge number of powers of 10 bigger than what we can see. Just from the Big Bang, parts of the Universe could be moving apart at much higher than the speed of light. This doesn’t violate the laws of physics; the Universe is stretching like a 3-D balloon (or lattice or raisin bread), and we can’t see those parts that are moving away faster than the speed of light relative to us. Although at any local point within the universe, nothing can travel faster than the speed of light, this is not true for the entire universe. There is no known limit on how fast space can expand. What is the bottom line? We have strong scientific evidence of a beginning and no end to the Universe. It began at a tiny point, is really, really, really huge, and will continue on expanding forever. It points to a Creation event. http://www.astro.ucla.edu/~wright/cosmo_02.htm
12
Measurements of parallax work out to about 1000 parsecs (1 parsec is about 3.26 light years).
Using Cepheid Variables to Measure Distance Cepheid variable stars are intrinsic variables which pulsate in a predictable way. In addition, a Cepheid star's period (how often it pulsates) is directly related to its luminosity or brightness.
1
Cepheid variables are extremely luminous and very distant ones can be observed and measured. Once the period of a distant Cepheid has been measured, its luminosity can be determined from the known behavior of Cepheid variables. Then its absolute magnitude and apparent magnitude can be related by the “distance modulus equation”, and its distance can be determined. Cepheid variables can be used to measure distances from about 1kpc to 50 Mpc (about 150 million light years). [So from this we know the Universe is at least millions of years old. Even if we were not convinced by Cepheid variables, we could simply look at a galaxy that is very far away and deduce that it is millions of light years away by how small it looks at its distance. We can see this effect even more with today’s telescopes, where we can resolve distant galaxies into their myriad stars. The Andromeda galaxy is roughly 2.4 million light years away. If the Universe were 6,000 years old, light from this galaxy would have only propagated 1/400 of the way towards Earth, and we would not see it at all.]
Using Type 1A Supernovae to Measure Distance Type 1a supernovae are all caused by exploding white dwarfs which have companion stars. The gravitational pull of the white dwarf causes it to take matter from its companion star. Eventually it reaches a high enough mass (about 1.44 solar masses) that it cannot support itself against gravitational collapse and explodes. [Some type 1a supernovae are caused by two white dwarf stars combining.] All type 1a supernovae reach nearly the same brightness at the peak of their outburst with an absolute magnitude of -19.3±0.03. They then follow a distinct curve as they decrease in brightness. So when astronomers observe a type 1a supernova, they can measure its apparent magnitude, knowing what its absolute magnitude is. They can then use the distance modulus equation to calculate the distance to the supernova, and the galaxy that it is in. Type 1a supernovae can be used to measure distances from about 1 Mpc to over 1000 Mpc (over 3 billion light years). [Actually astronomers are able to do this past 10 billion light years now.] 2
So we can measure the distances of objects out to huge distances. And what we find is that the further away things are, the faster they are moving away from us.
How do we figure out how they are moving, towards or away from us?
(from University of Nebraska-Lincoln website)
(Spectra of stars, from University of Nebraska-Lincoln website)
3
The Doppler Effect (from Cornell University website)
The Expansion of the Universe Edwin Hubble discovered that the universe is expanding when he found that the further away a galaxy was, the more its spectral lines were redshifted. So nearby galaxies are moving away from us slowly, and far away galaxies are moving away much more quickly. Their apparent motion isn’t due to their motion through space, but the expansion of space itself. Graph from: http://www.google.com/imgres?imgurl=http://www.uni.edu/morgans/astro/course/Notes/ section3/hubblelaw.gif&imgrefurl=http://www.uni.edu/morgans/astro/course/Notes/sectio n3/new13.html&h=301&w=421&sz=5&tbnid=5JEigeUUXPd8M:&tbnh=82&tbnw=115&prev=/search%3Fq%3Dgalaxy%2Bdistance%2Bversus%2Bs peed%26tbm%3Disch%26tbo%3Du&zoom=1&q=galaxy+distance+versus+speed&usg= __TPMgTi0KUd_HUHYfwET538G71c4=&sa=X&ei=wdF4UNP_OZO89QS4vIAQ&ved= 0CCgQ9QEwBA A Hubble Diagram, simply a plot of galaxy velocity versus galaxy distance (using supernovae).
4
The expanding universe can be compared to what happens when a loaf of bread with raisins in it bakes and expands in an oven. As the bread rises and expands, the raisins seem to move away from each other. They are not moving within the dough, but as the dough expands, the distance between them becomes greater. In this scenario, a raisin on one edge of the bread would see raisins on the opposite side of the bread moving away with a greater speed than nearby raisins. Or (from Edward Lu website) you can look at it as an expanding lattice (a print by Escher):
As far as the eye can see, the grid goes on forever. Now imagine each of the sticks between nodes all getting longer. The nodes separate, and this Escher universe expands. But it isn’t expanding into anything, it is just getting larger. That’s exactly the same as what we notice about our own universe. All the galaxies appear to be moving away from each other. But there is no edge to the universe, and therefore there also isn’t a center to the universe (which is also the reason the Big Bang didn’t happen at a point). At least we haven’t seen an edge yet.
We mainly believe there is no edge or center because there is no evidence of a central place. From any vantage point, everything looks like it is moving away.
From Wikipedia (big bang):
The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe.[1] According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state. According to the most recent measurements 5
and observations, the Big Bang occurred approximately 13.75 billion years ago, [2][3] which is thus considered the age of the Universe.[4][5] After its initial expansion from a singularity, the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and electrons. While protons and neutrons combined to form the first atomic nuclei only a few minutes after the Big Bang, it would take thousands of years for electrons to combine with them and create electrically neutral atoms. The first element produced was hydrogen, along with traces of helium and lithium. Giant clouds of these primordial elements would coalesce through gravity to form stars and galaxies, and the heavier elements would be synthesized either within stars or during supernovae. The Big Bang is a well-tested scientific theory and is widely accepted within the scientific community. It offers a comprehensive explanation for a broad range of observed phenomena. Since its conception, abundant evidence has been uncovered in support of the model. [6] The core ideas of the Big Bang—the expansion, the early hot state, the formation of helium, and the formation of galaxies—are derived from many observations that are independent from any cosmological model; these include the abundance of light elements, the cosmic microwave background, large scale structure, and the Hubble diagram for Type Ia supernovae. [All these things match what is expected for a Universe that came from the Big Bang.] As the distance between galaxy clusters is increasing today, it can be inferred that everything was closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures,[7][8][9] and large particle accelerators have been built to experiment in such conditions, resulting in further development of the model. On the other hand, these accelerators have limited capabilities to probe into such high energy regimes. There is little evidence regarding the absolute earliest instant of the expansion. Thus, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on. Georges Lemaître first proposed what would become the Big Bang theory in what he called his "hypothesis of the primeval atom." Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions such as homogeneity and isotropy of space. The governing equations had been formulated by Alexander Friedmann. In 1929, Edwin Hubble discovered that the distances to far away galaxies were generally proportional to their redshifts— an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity. [10] While the scientific community was once divided between supporters of the Big Bang and those of alternative cosmological models, most scientists became convinced that some version of the Big Bang scenario best fit observations after the discovery of the cosmic microwave background radiation in 1964, and especially when its spectrum (i.e., the amount of radiation measured at each wavelength) was found to match that of thermal radiation from a black body. Since then, astrophysicists have formulated further hypotheses to account for some discrepancies that have arisen within the model. 6
The cosmic background radiation is a strong confirmation. It was predicted to be a result of the Big Bang, the radiation released at about 380,000 years after the Big Bang, when the universe thinned sufficiently so that the photons could travel without being absorbed. It was at just the right temperature as expected, when its spectrum was adjusted for the long distance away. Its texture is correct for the kinds of variations that led to the formation of galaxies.
(from NASA website) Will the Universe expand forever or collapse on itself? Initially, two teams of scientists (1998) discovered from observing Type 1a supernovae, that the universe appeared to be expanding at an increasing rate. Rather than a linear increase (with distance) in expansion as expected, or a reduced expansion in recent times due to gravity slowing the expansion down, the more recent (closer) objects are moving away faster than they should be, indicating that the expansion is speeding up. The evidence was somewhat sparse, with not very many supernovae observed. More evidence has occurred in more recent years:
Sloan survey shows dark energy who's boss Based on new, more accurate measurements of distant galaxies, astronomers believe the expansion of the universe started accelerating some 5 to 7 billion years ago. By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts — Published: March 30, 2012
7
The record of baryon acoustic oscillations (white circles) in galaxy maps helps astronomers retrace the history of the expanding universe. These schematic images show the universe at three different times. The representative-color image on the right shows the "cosmic microwave background," a record of what the young universe looked like 13.7 billion years ago. The small density variations present then have grown into the clusters, walls, and filaments of galaxies that we see today. These variations included the signal of the original baryon acoustic oscillations (white circle, right). As the universe has expanded (middle and left), evidence of the baryon oscillations has remained, visible in a "peak separation" between galaxies (the larger white circles). The SDSS-III results announced today (middle) are for galaxies 5.5 billion light-years distant, at the time when dark energy turned on. Comparing them with previous results from galaxies 3.8 billion light-years away (left) measures how the universe has expanded with time. Credit: E.M. Huff/the SDSS-III team/South Pole Telescope team. Graphic by Zosia Rostomian
[Distances between galaxies is larger than it would be if the expansion were not accelerating.] Astronomers have made the most accurate measurement yet of galaxy distances in the faraway universe, giving an unprecedented look at the time when dark energy turned on. Some 5 to 7 billion years ago, the expansion of the universe stopped slowing due to gravity and started to accelerate due to dark energy. Yet the nature of dark energy remains a puzzle that astronomers are seeking to solve. The new measurement came from the Baryon Oscillation Spectroscopic Survey (BOSS), which is part of the third Sloan Digital Sky Survey (SDSS-III). "We see the influence of dark energy on cosmic structure, but we have no idea what it is. The data gathered by this survey will help answer that question," said Daniel Eisenstein from the HarvardSmithsonian Center for Astrophysics in Cambridge, Massachusetts. "There's been a lot of talk about using galaxy maps to find out what's causing accelerating expansion," said David Schlegel from the U.S. Department of Energy's Lawrence Berkeley National Laboratory in California, BOSS's principal investigator. "We've been making a map, and now we're using it — starting to push our knowledge out to the distances when dark energy turned on." Investigating Dark Energy One of the most amazing discoveries of the last two decades in astronomy, recognized with the 2011 Nobel Prize in physics, was that not only is our universe expanding, but it also is accelerating. Galaxies are becoming farther apart from each other faster and faster with time. The leading contender for the cause of the accelerating expansion is a postulated new property of space dubbed "dark energy." Alternatively, the universe may be accelerating because gravity deviates from Einstein's general theory of relativity and becomes repulsive at very large distances. Whether the answer to the puzzle of the accelerating universe is dark energy or modified gravity, the first step to finding that answer is to measure accurate distances to as many galaxies as possible. From those measurements, astronomers can trace out the history of the universe's expansion. BOSS is producing the most detailed map of the universe ever made by using a new custom-designed spectrograph of the SDSS 2.5-meter telescope at Apache Point Observatory in New Mexico to observe more than a million galaxies over six years.
8
The astronomers' announcement is based on a map of more than 250,000 galaxies created from the first year and a half of BOSS observations. Some of these galaxies are so distant that their light has traveled more than 6 billion years to reach Earth — nearly half the age of the universe. Surveying the Cosmos Maps of the universe like BOSS's show that galaxies and clusters of galaxies are clumped together into walls and filaments, with giant voids between. These structures grew out of subtle variations in density in the early universe, which bore the imprint of "baryon acoustic oscillations" — pressure-driven acoustic (sound) waves that passed through the early universe. [Baryons are particles made up of three quarks. The most familiar baryons are protons and neutrons.] Billions of years later, the record of these sound waves can still be read in our universe. "Because of the regularity of the ancient sound waves, there's a slightly increased probability that any two galaxies today will be separated by about 500 million light-years, rather than 400 million or 600 million," said Eisenstein. In a graph of the number of galaxy pairs by separation distance, that magic number of 500 million lightyears shows up as a peak, so astronomers often speak of the "peak separation." The position of this peak depends on the amount of dark energy in the universe. But measuring the distance between galaxies depends critically on having the right distances to the galaxies in the first place. That's where BOSS comes in. "We've detected the peak separation more clearly than ever before," said Nikhil Padmanabhan of Yale University. "These measurements allow us to determine the contents of the universe with unprecedented accuracy."
Cosmic acceleration, further evidence
"Cosmic mirages" confirm accelerated cosmic expansion These results independently indicate that the expansion of the universe is accelerating, which suggests that the universe must be filled with a mysterious energy component called dark energy. By University of Tokyo, Kashiwa, Japan — Published: April 11, 2012
9
Image of SDSSJ12260006, a new gravitationally lensed quasar discovered in this survey. The quasar image in the original image of the Sloan Digital Sky Survey, which has been used for the actual survey to identify gravitational lensing, looks only slightly extended, but the Hubble Space Telescope image clearly exhibits two distinct quasar images (white) as well as a massive galaxy in between the quasar images (orange) that produces gravitational lensing.
Quasars are luminous objects powered by accretion of gas into supermassive black holes at the centers of distant galaxies. A quasar is typically located far away. Gravitational lensing is a phenomenon in which a distant object is split into two or more images due to the gravity of a massive foreground object. The phenomenon of gravitational lensing, often called a “cosmic mirage”, was first discovered in 1979, and since then more than 100 gravitationally lensed quasars have been reported. An international team of researchers led by Masamune Oguri and Naohisa Inada from the Nara National College of Technology in Japan conducted a large survey to search for gravitationally lensed quasars in the massive data sets of the Sloan Digital Sky Survey (SDSS). During almost 10 years of careful examinations of 100,000 quasars, the team successfully discovered nearly 50 new gravitationally lensed quasars in total, significantly increasing a sample of cosmic mirages. The frequency of gravitational lensing, which can be measured by counting the number of gravitationally lensed quasars within a given quasar catalog, allows one to infer the expansion speed of the universe because the accelerated expansion increases the distance to each quasar and, therefore, enhances the chance of gravitational lensing. The team measured the probability of gravitational lensing among distant quasars to be about 0.05 percent, which was then compared with detailed theoretical calculations to extract information on the expansion history. The result indicates that the expansion of the universe is indeed accelerating, which suggests that the universe must be filled with a mysterious energy component called dark energy.
10
Illustration of the gravitational lensing measurement of the cosmic expansion speed. The accelerated expansion increases the distance to the quasar, giving rise to higher chance of having a massive galaxy close to the light path to produce gravitational lensing. Credit: Kavli IPMU
“The accelerated cosmic expansion is one of the central problems in modern cosmology,” Oguri said. “In 2011, the Nobel Prize in physics was awarded to the discovery of the accelerated expansion of the universe using observations of distant supernovae. A caution is that this method using supernovae is built on several assumptions, and therefore independent checks of the result are important in order to draw any robust conclusion. Our new result using gravitational lensing not only provides additional strong evidence for the accelerated cosmic expansion, but also is useful for accurate measurements of the expansion speed, which is essential for investigating the nature of dark energy.” Careful comparisons with other cosmological observations led to the conclusion that dark energy behaves almost like Einstein’s cosmological constant. [Einstein and others believed that the Universe must be static. He inserted a “cosmological constant” in his equations to make this happen. Many scientists initially rejected the Big Bang theory because it implies the Universe had a beginning. The evidence eventually became overwhelming.] “Statistical methods on gravitationally lensed quasars have been known to be sensitive to the expansion history of the universe,” Masashi Chiba from Tohoku University said, “therefore actively studied by Japanese researchers in the 1990s. Observations of gravitational lensing at that time already hinted at the presence of dark energy, but both due to the small sample size and large uncertainty in the theoretical modeling of lensing rates, the result was not widely accepted. This research conducted an enormous survey of gravitationally lensed quasars and adopted much more sophisticated theoretical calculations to build a very convincing case for the accelerated cosmic expansion.” “Studies of dark energy — cosmological constant — were popular in Japan already in the early 1990s, largely because of pioneering work by Fukugita,” said Yasushi Suto from the University of Tokyo. “This survey of gravitationally lensed quasars was initiated and organized by Oguri and Inada, who were graduate students when the survey started, within the large international SDSS collaboration, and they led the team to success. This result is important in that it confirms the presence of dark energy independently from the observation of supernovae.”
11
Detailed properties of dark energy are planned to be explored in the SuMIRe project, an international survey project led by Kavli IPMU using the Subaru Telescope. “This result demonstrates that Japanese theoretical and observational cosmologists will play an essential role in the SuMIRe project,” Suto said. “This result creates big momentum for the survey of the cosmic dark energy by the SuMIRe project,” Chiba said. [So we have looked at three methods which all indicate that the Universe’s expansion rate is increasing.] ---------------------------------------------------------------------------------
The Universe is much larger than 13.7 billion light years across, one reason being that the objects that emitted light that reached us 13.7 billion years later are now much farther away. But the Universe could be much bigger than that, in fact it could be infinite, or a huge number of powers of 10 bigger than what we can see. Just from the Big Bang, parts of the Universe could be moving apart at much higher than the speed of light. This doesn’t violate the laws of physics; the Universe is stretching like a 3-D balloon (or lattice or raisin bread), and we can’t see those parts that are moving away faster than the speed of light relative to us. Although at any local point within the universe, nothing can travel faster than the speed of light, this is not true for the entire universe. There is no known limit on how fast space can expand. What is the bottom line? We have strong scientific evidence of a beginning and no end to the Universe. It began at a tiny point, is really, really, really huge, and will continue on expanding forever. It points to a Creation event. http://www.astro.ucla.edu/~wright/cosmo_02.htm
12
