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----------------------------- 2698 - REDSHIFT - explains the Universe expansion?
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- The Redshift is defined as the increase in wavelength of electromagnetic radiation received by a detector compared with the wavelength of the emitting source. It is the same as the Doppler shift that you are familiar with in sound waves.
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- When the source and the receiver are moving away from each other the wavelengths get stretched out and become longer. Sound becomes lower pitched and light becomes “redder”, shifting to longer wavelengths, or lower frequencies. If the source and the receiver were moving toward each other it would be a Blueshift and wavelengths would shorten.
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- Redshifts can occur due to Doppler effects, Relativistic effects, Expansion of the Universe effects, or Gravitational effects. We are only going to address the effects of the expansion of the Universe in this review.
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- The first galaxy discovered to have a Redshift was the Sombrero Galaxy (M104). This was in 1912 at the Lowell Observatory in Arizona. Like most galaxies the Sombrero contains sodium atoms. When light travels through the sodium an atom will become excited and absorb a particular frequency, or wavelength of light.
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- This exact wavelength of photon energy is the exact amount of energy to excite a sodium electron into a higher energy shell. The atom absorbs that particular wavelength photon as it goes into the excited state. When the electron returns, or falls back, into the lower energy state it will emit that same wavelength photon.
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- In the case of absorption when astronomers receive the light spectrum they detect a dark line where the wavelength of light has been absorbed by the sodium atoms.
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- When astronomers measured the wavelength absorbed coming from the Sombrero Galaxy it was at 591 nanometers. But, astronomers know that the actual sodium absorption wavelength should be 589 nanometers.
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- So, what caused the wavelength to get slightly longer when it got to Earth? The measured wavelength is 0.34% longer than the expected wavelength. (591 / 589 ). This 0.34% longer wavelength is caused by the expanding distance between Earth and the Sombrero Galaxy. The Galaxy appears to be moving away from us and the amount of the Redshift is 0.0034.
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- For small Redshifts you can calculate the velocity of the separation by multiplying the Redshift by the speed of light. ( This will not work for large Redshifts because at higher velocities you have to take into account the Theory of Relativity.)
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--------------- The speed of light --------------- 670,633,500 miles per hour.
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--------------- The Redshift -------------------- 0.0034
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--------------- The receding speed of the Galaxy ----- 2,280,000 miles per hour.
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- For small Redshifts the distance to the source can be calculated by multiplying the Redshift by 14,000,000,000 light years:
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--------------- The Redshift --------------------- 0.0034
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--------------- The distance to Galaxy -------- 47,600,000 lightyears away.
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- For the Sombrero Galaxy the Universe has stretched 1.0034 times since the light we see today left the galaxy to begin with. At that time the light left the galaxy the Universe was 99.7% its current age. ( 1/1.0034). As you can see the Universe had not expanded very much during the time the light left the Sombrero Galaxy until it reached us on Earth.
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- But, the formulas do not work when the Redshifts are larger. For example: When the Redshift of a distrant galaxy cluster is measured the Redshift is 1.4. If we take 1.4 times the speed of light we get the galaxy cluster moving faster than the speed of light, and that can not happen without considering the Theory of Relativity:
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--------------- Redshift = 1.4
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--------------- Velocity / speed of light = z^2 +2z / z^2 + 2z + 2
--------------- Where “z” is the Redshift
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--------------- 1.4^2 + 2.8 / 1.4^2 + 2.8 + 2 = 4.76 / 6.76
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--------------- 70%, the velocity of the galaxy cluster is receding at 70% the speed of light. A more accurate expression is that the space between us and the galaxy cluster is expanding at 70% the speed of light.
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-------------- The look back time is 9,000,000,000 years
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-------------- The co-moving distance is 13,000,000,000 lightyears.
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------------- The Universe we see is 42% its current age
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-------------- The Universe is 5,750,000,000 years old at the time the light left this galaxy cluster.
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- Let’s measure the Redshift of a greater distant Quasar, one of astronomy’s most distant objects.
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--------------- Redshift = 5.8
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-------------- The look back time is 12,500,000,000 years
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-------------- The co-moving distance is 27,000,000,000 lightyears.
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------------ The Universe is 9% its current age
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-------------- The Universe is 1,200,000,000 years old at the time the light left the Quasar.
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- The reason distance gets so ambiguous is that during the time it took the light to get here the Universe was expanding at an ever increasing rate and the distances have accelerated their rate of growth. Astronomers call this the co-moving distance since the object and the observer are co-moving apart from each other.
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- So, if you took a ruler today and measured the distance it would be 27,000,000,000 light years. But, back when the light was emitted in the Redshift you saw the distance was 4,000,000,000 light years. But, if you sat on the light beam and measured the actual distance you traveled it would be 12,500,000,000 lightyears, and that distance is equivalent to the look back time, 12,500,000,000 years. The Universe was 1,200,000,000 years old at that time.
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- Let’s us a baseball analogy: The pitcher is 60.5 feet from home plate. The center fielder is 300 feet from home plate. In one second the scale of the baseball field doubles. Now the pitcher is at 121 feet and the center fielder is at 600 feet. The picture moved 60.5 feet / second or 41 miles per hour. The center fielder moved 300 feet / second or 205 miles per hour. The farther distance away the faster the velocity.
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- The same thing happens with galaxies, the farther away they are the faster they appear to be moving away from us. Of course, the center fielder feels that he is standing still and home plate is moving away from him at 205 miles per hour. Everything around him is moving away so he thinks he is in the center of the Universe.
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- And, if the fly ball is rotating 1000 times in its path from home plate to center field and the rate of the field’s expansion continues the rotation rate of the ball will appear to slow down. The distance traveled per rotation will appear to become longer, that is the wavelength lengthens, the “Redshift” increases.
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- When the rate of the field expansion equals the velocity of the ball, the ball appears to stop in mid-air. Time itself stops. Likewise, when anything approaches the speed of light time slows down until it stops. Photons do not experience time.
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- The longest Redshift astronomers have recorded is for the Cosmic Microwave Background Radiation.
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----------------- Redshift = 1,089
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----------------- The look back time = 13,700,000,000 years
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----------------- The co-moving distance is 46,000,000,000 lightyears.
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---------------- The Universe is 0.09% of its current age. That is about 0.1%, so, since that time the Universe has expanded 1000 times. And, the wavelength has lengthened by 1000 times. The wavelength of light leaving the opaque surface of the Universe at that time when it was 380,000 years old was 1,849 nanometers, which is the wavelength of Gamma Rays.
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- The wavelength of the light (microwaves) we receive today is 2,000,000 nanometers, the frequency of 150 Gigahertz, which is in the microwave frequency range. The thermal energy of this radiation is 2.725 Kelvin. This is very close to absolute zero, just 3 degrees above it. When it left the source the temperature was 3,000 Kelvin. So, the temperature as cooled by 1000 times as well.
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- The look back distance in lightyears represents the Observable Universe that we can see. There is a Universe beyond our Observable one. When the co-moving distance is greater than the look back distance the object will eventually recede beyond the Observable Universe and will disappear forever.
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- Measuring Redshifts has taught us a lot about our Universe. To learn more read about spectroscopy. This is the technique of putting light through a prism, spreading out the constituent wavelengths, and analyzing the emission and absorption lines that are created when the light goes through the elements.
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- By looking at the spectrum from the Sun astronomers discovered the element helium, before it we discovered here on Earth.
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- April 5, 2020 835 2698
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--------------------- Sunday, April 5, 2020 -------------------------
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