Almost all galaxies are observed to have redshifts. The universe is expanding, and this “cosmological redshift” causes the light from distant galaxies to be stretched (made redder) during the time it travels from the galaxy to our telescopes due to the expansion of the intervening space.
A blueshift is any decrease in wavelength (increase in energy), with a corresponding increase in frequency, of an electromagnetic wave; the opposite effect is referred to as redshift. In visible light, this shifts the color from the red end of the spectrum to the blue end. Galaxies moving toward us are blueshifted.
Edwin Hubble’s* interpretation was in terms of recession of these galaxy clusters through space and the recession velocity can be calculated from the Doppler formula, z = v/c.
As the recession velocity of the most distant, Hydra, is only about 20% of the speed of light, the non-relativistic approximation is reasonably good, although it would be useful to carry out the calculations to check, yielding a difference of about 20%.
The distances to galaxies are determined using redshift. The information comes to us through light as transmitted via photons. The distances are calculated using the shifts in absorption lines via Hubble's Law of Expansion (v=HD) and the Energy of Photon (E=hc/wavelength) equations.
The question is "does the energy of a photon dissipate through time and/or interference with inter-gallactic matter?" If not, how is this known? If so, could that not account for redshift? If it is true, then how is it KNOWN what the dissipation would be? Obviously, were any of this to be true then location of far-away galaxies could explained other than by expansion of the universe. If energy does not dissipate then a photon in a space otherwise a vacuum should remain at a constant energy level eternally.
The theory of inflation of space-time which is posited to have occured faster than the speed of light (not measurible or falsifiable!). Supposing this to have occured, and having occured early in the universe's history, why the vast emptiness of space? Surely the expansion would have happened evenly within the primordial clouds of "gas" that existed before the formation of galaxies and clusters rather than in quantized/preferred portions of space to allow that clustering. If this were so, then there would be less space between galaxies and the later clusterings would have been into smaller objects.
Assuming that early galaxies had formed, then the expansion would have happened within them as well rather simply between them. This would stretch the galaxies as well as the intervening space-time. It does not.
Redshift is shown to have relativistic effects upon it near a black-hole. Similarly the most distant visible galaxies are receding at near speed of light. Wouldn't the redshift from those galaxies have a similar relativistic effect upon it? Items near an event horizon undergo an "apparent" time dilation effect due to relative speeds. Would this not be true for galaxies receding nearer the edge of the visible universe? If so, then they should appear to be receding slower than they actually are. Meaning, that galaxies receding from us closer in would appear to be receding faster than they should be relative to the speeds of distant galaxies. This would make the expansion of the universe to appear to have sped up more recently than the long ago expansion.
It is assumed that the dark energy is constant with volume and that as space time expands it expands with it, thus creating more "pressure" with time. It is not a measurable quantity, but rather is an artifact of the equations used with the cosmological constant.
Another more modern way of interpreting the redshift is in terms of expansion of the Universe. In this case, the redshifts allow us to calculate by what factor the Universe has expanded since the light was emitted using the equation
z + 1 = R (now)/R (emission)
so that putting z = v/c, the light from Virgo was emitted when the Universe was about 0.3% smaller than it is now.
The below chart shows varying red shifts:
The below chart shows the cosmological red shift as being proportional to the expansion of space itself:
These spectra show increasing redshift with distance. You can make an interesting teaching point about the different ways of interpreting this red shift. Hubble’s interpretation was in terms of recession of these galaxy clusters through space and the recession velocity can be calculated from the Doppler formula, z = v/c. As the recession velocity of the most distant, Hydra, is only about 20% of the speed of light, the non-relativistic approximation is reasonably good, although it would be useful to carry out the calculations to check, yielding a difference of about 20%.
You may also interpret the red shift in terms of expansion of the Universe. In this case, the red shifts allow us to calculate by what factor the Universe has expanded since the light was emitted using the equation
z + 1 = R (now)/R (emission)
so that putting z = v/c, the light from Virgo was emitted when the Universe was about 0.3% smaller than it is now.
These spectra provide evidence that can be interpreted in more than one way: either as due to recession of distant galaxies due to their speed away from us, or as due to an expansion of space-time. This illustrates that the ways that data are interpreted are inevitably influenced by current theoretical models.
There are a few alternative theories:
Tired light theories.
LOCAL Cosmic Microwave Background patches.
Quantum FOAM attenuation and/or diffraction of Light.
Quantum Time distortions of Light.
Gravitational distortions of Light.
While there are counter arguments against them, any doubts about red shift would have to also counter the Cosmic Microwave background and Wimap energy maps of the early universe.
There's also a direct redshift-distance test we can perform to determine whether the redshift is due to a Doppler motion or to an expanding Universe. There are different ways to measure distance to an object, but the two most common are as follows:
angular diameter distance, where you know an object's physical size and infer its distance based on how large it appears,
or luminosity distance, where you know how bright an object intrinsically is and infer its distance based on how bright it appears.
When you look out at the distant Universe, the light has to travel through the Universe from the emitting object to your eyes. When you do the calculations to reconstruct the proper distance to the object based on your observations, there's no doubt: the data agrees with the expanding Universe's predictions, not with the Doppler explanation.
The first is to look at the surface brightness of distant galaxies. If the Universe weren't expanding, a more distant galaxy would appear fainter, but a uniform density of galaxies would ensure we were encountering more of them the farther away we look. In a Universe where the light got tired, we would get a constant number density of photons from progressively more distant galaxies. The only difference is that the light would appear redder the farther away the galaxies are.
This is known as the Tolman Surface Brightness test, and the results show us that the surface brightness of distant galaxies decreases as a function of redshift, rather than remaining constant.
Additionally, the 2dF redshift survey used the two-degree field spectroscopic facility on the Anglo-Australian Telescope to measure the redshifts of approximately 220,000 galaxies during 1995 to 2002. This advanced the state of the art in large-scale structure by an order of magnitude in survey size, permitting a wide range of fundamental advances in cosmology. All data were released in July 2003.
The input catalogue contains 250 000 galaxies, for which 81 895 have been observed using 2dF (as of 1999 November). Each spectrum within the data base has been examined by eye to check if the redshift is reliable. Redshifts are determined via cross-correlation with specified templates (see Folkes et al. 1999 for details). A brief test of the reliability of the 2dFGRS was achieved via a comparison between 1404 galaxies in common with the Las Campanas Redshift Survey (Lin et al. 1996), for which there were only eight mismatches, showing that 2dF redshifts are reliable. Of the 81 895 galaxies, 74 562 have a redshift, resulting in a redshift completeness of 91 per cent.
If we lived in a Universe where the distant galaxies were so redshifted because they were moving away from us so quickly, we'd never infer that an object was more than 13.8 billion light-years away, since the Universe is only 13.8 billion years old (since the Big Bang). But we routinely find galaxies that are 20 or even 30 billion light-years distant, with the most distant light of all, from the Cosmic Microwave Background, coming to us from 46 billion light-years away.
I'm hoping that the information above has answered most of questions about the galactic redshift. Kindly bring up any further questions on the galactic redshifts and how their measurement began with Edwin Hubble, a true giant in astronomy.
* Edwin Hubble, for whom the Hubble Space Telescope is named, was one of the leading astronomers of the twentieth century. His discovery in the 1920s that countless galaxies exist beyond our own Milky Way galaxy revolutionized our understanding of the universe and our place within it.
Hubble, a tall and athletic man who excelled at sports and even coached high school basketball for a short while, started his professional science career during one of the most exciting eras of astronomy. It was 1919, just a few years after Albert Einstein published his theory of general relativity, and bold, new ideas about the universe were fermenting. Hubble was offered a staff position at the Mount Wilson Observatory, which housed the
newly commissioned 100-inch Hooker telescope, then the largest telescope in the world. Hubble, it seemed, had the universe placed in his lap.
Most astronomers of Hubble's day thought that all of the universe — the planets, the stars seen with the naked eye and with powerful telescopes, and fuzzy objects called nebulae — was contained within the Milky Way galaxy. Our galaxy, it was thought, was synonymous with the universe.
In 1923 Hubble trained the Hooker telescope on a hazy patch of sky called the Andromeda Nebula. He found that it contained stars just like the ones in our galaxy, only dimmer. One star he saw was a Cepheid variable, a type
of star with a known, varying brightness that can be used to measure distances. From this Hubble deduced that the Andromeda Nebula was not a nearby star cluster but rather an entire other galaxy, now called the Andromeda galaxy.
In the following years he made similar discoveries with other nebulae. By the end of the 1920s, most astronomers were convinced that our Milky Way galaxy was but one of millions in the universe. This was a shift in thought as profound as understanding the world was round and that it revolved around the sun.
Hubble then went one step further. By the end of that decade he had discovered enough galaxies to compare to each other. He created a system for classifying galaxies into ellipticals, spirals and barred spirals — a system called the Hubble tuning fork diagram, used today in an evolved form.
But the most astonishing discovery Hubble made resulted from his study of the spectra of 46 galaxies, and in particular of the Doppler velocities of those galaxies relative to our own Milky Way galaxy. What Hubble found was that the farther apart galaxies are from each other, the faster they move away from each other. Based on this observation, Hubble concluded that the universe expands uniformly. Several scientists had also posed this theory based on Einstein’s General Relativity, but Hubble's data, published in 1929, helped convince the scientific community.
Hubble and his colleague at Mt. Wilson, Milton Humason (who started as a mule driver during the construction of the observatory, then janitor, then night assistant), estimated the expansion rate of the universe to be 500 kilometers per second per megaparsec. (A megaparsec, or a million parsecs, is a distance equal to about 3.26 million light-years; so a galaxy two megaparsecs away is receding from us twice as fast as a galaxy only one megaparsec away.) This estimate is called the Hubble Constant, and scientists have been fine-tuning it ever since.
The Hubble Space Telescope was launched in 1990, one of its major goals being to pin down the Hubble Constant. In 2001, a team studying supernovae with Hubble, along with ground-based optical telescopes, established a rate of 72 ± 8 km/sec/Mpc. In 2006, a team studying the cosmic microwave background with NASA's WMAP satellite tweaked this measurement to 70 km/sec/Mpc. Hubble, the telescope, also helped discover that not only is the universe expanding, the expansion is accelerating. The mysterious force causing this acceleration is dubbed dark energy.
Hubble was born on November 20, 1889, in Marshfield, Missouri, and moved to Wheaton, Illinois, before his first birthday. He studied mathematics and astronomy at the University of Chicago and earned a bachelor of science degree in 1910. He was one of the first Rhodes Scholars at Oxford University, where he studied law. After serving briefly in World War I, he returned to the University of Chicago and earned his doctorate degree in 1917. After a long career entirely at Mt. Wilson Observatory, he died of a heart attack on September 28, 1953, in San Marino, California. As with the telescope that bears his name, Edwin Hubble transformed our understanding of the universe. His spirit of discovery lives on today in the Hubble Space Telescope.
In a few more years, when all cars are equipped with radars, people MIGHT start to see that light does not behave like sound.
Every car will have a multi-directional radar. And see with their own eyes that reflected light is different than emitted light.
Our present science tells us that a reflection, can be considered to be an emission source. This is bad juju.
Scenario one. Stationary radar gun on side of road. Radar transmission F is 10 GHz. Car is approaching at 70 MPH. For the sake of simple example, the echo or bounce F is 10.1 GHz. An increase in F, a blue shift.
Scenario two. Stationary radar gun on side of road. But no transmitter, just a receiver. The car is approaching at 70 MPH. The car has a 10 GHz transmitter. What F will the radar gun receive? Will it be 10.1 GHZ because the car is coming at you at 70 MPH? Or will you receive a 10 GHZ signal from the transmitter?
Our science only thinks it knows what light is. It's just as puzzling as ever.