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- The Universe is much, much larger than our “Observable Universe”. We can only see as far as light has traveled this past 13,500,000,000 years. But, that is in both directions so we can theoretically be looking at two regions in space that are 27,000,000,000 lightyears apart.
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- There is a lot to see in our Observable Universe. How do we measure how big it is? We measure the brightness of a distant light source, a galaxy, and calculate its distance by how much dimmer it has gotten as the light beams spread out across the Universe. The further the light source is away the dimmer it will appear. It is a fairly simple formula:
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------------------------ Apparent Brightness = Sources luminosity / 4 * pi * d^2
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--------------------------- 4*pi*d^2 is the surface area of a sphere.
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- If we know the luminosity, how intrinsically bright the object is, and , we measure the apparent brightness from Earth, then, we calculate the distance, “d”, to learn how far away it is.
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- The luminosity is the total power the source emits into space. The power dissipates as it radiates in all directions.
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- Obviously this formula has some limitations. How do we know the intrinsic luminosity of the source? All galaxies, or stars, are not the same. How do we know if dust in the interstellar space between us has not dimmed the light. We make assumptions and we calculate distances with inherently large uncertainties.
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- Is there a better way to measure these cosmic distances?
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- One possibility involves Baryon Oscillation Spectroscopy. Baryons are the scientific name for all atoms without electrons. The electrons are called Leptons. When separated the Baryons can carry positive charges, protons, and , the Leptons carry negative charges. The Baryons, protons and neutrons, are 1,800 times heavier than the electrons although their charges are equal.
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- Before atoms first formed in the hot plasma of the early Universe these charged particles, baryons, interacted with the photons of light. The expanding waves of these interactions traveled 60% the speed of light, like sound waves but much faster.
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- The wave action was created by the repeated interaction between the pull of gravity due the mass of the baryons and the push of the radiation pressure of expansion. The wave action continued for 380,000 years until the Universe expansion cooled enough for the baryons and the electrons to begin combining and forming neutral atoms, hydrogen and helium.
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- Neutral atoms are immune to light photons that are pushing the radiation pressure. We see the free photon radiation cooled from 3,000 degrees Kelvin then down to 3 degrees Kelvin today. Today this is the Cosmic Microwave Background radiation. The wavelengths stretched as space expanded over the past 13.5 billion years. Light stretched into microwaves.
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- What astronomers are anxious to be able to do is to measure the size of the waves of Baryon Oscillation. By knowing the wavelengths and the speed of these oscillations astronomers can re-calculate cosmic distances.
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- The wavelengths of the Cosmic Microwave Background are about 1 arc degree in the sky. This 1 arc degree translates to 490 million lightyears distance. ( 150 mega parsecs ).
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- The average separation of galaxies in the Universe matches this 490 million lightyears. But, that is the average. Galaxies have been jostled around to where the spread varies from 140 to 160 mega parsecs, averaging 150 mega parsecs.
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- If astronomers can measure the Baryon Oscillation wavelengths they would have another cosmic ruler in 3-dimensions., not just 2-dimensions. To this end astronomers have measured the separation distances of 46,748 pairs of galaxies as part of the earlier Sloan Digital Sky Survey.
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- Using the latest Baryon Survey they have measure 1,200,000 galaxies distances with 1% accuracy. One calculation that falls out of this is the rate of the expansion of the Universe. The Hubble Constant is calculated to be 67 kilometers per second per mega parsec.
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- Translating this to more familiar terms, the expansion of space is occurring at 47,000 miles per hour separation speed for every 1 million lightyears separation. Space is expanding. The more space between the galaxies the faster they are separating.
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- So now we have another means besides light, the electromagnetic spectrum, in which to study the Universe. We have the waves of charged particles. There may be even another cosmic ruler using the waves of gravity.
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- All these methods involve the movement of energy. With electromagetics the higher the frequency of oscillation the higher the energy:
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---------------------------- E = h * f
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- With gravity the higher the mass the greater the force, energy of gravity.
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---------------------- E = m*M / r^2
---------------------- E = F / r
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- “r” is distance and on the scale of the Universe gravity dominates. Dominates along with Dark Energy which is some unknown energy causing the expansion. How can we see the oscillating waves of gravity? How can measure the wavelengths of gravity waves? The energy of gravity is very weak on the worldly scale. A magnet can hold a paper clip with the gravity of the entire Earth pulling it down.
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- Einstein’s theories have gravity as a distortion in the dimensions of space and time. His General Relativity theory would have sudden changes in the curvature of spacetime create waves propagating across the Universe.
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- The problem is that the gravity waves are so weak we can not detect them. They travel at the speed of light. When they pass through a mass the mass would experience a small compression and expansion as the wave moves through. But, unless the mass is enormous the changes are undetectable.
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- We have some indirect evidence from observing two binary Neutron Stars that are orbiting each other. Observations from 1975 to 2014 have seen the orbits decay by 15 seconds. These whirling, enormous masses emit gravity waves causing their orbits to steadily decay. Theory calculations match observation giving indirect evidence that gravity waves exist.
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- If a gravity wave passed Earth we should see a slight distortion of spacetime in one direction then the other as the wave passed by. A mass would distort in the left to right direction then in the top to bottom direction as the wave passes. Believe it or not astronomers think they can measure this. Here is one proposal:
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- Pulsars are spinning Neutron Stars. They can spin at millisecond rates. A pair of pulsars close together might be detected as millisecond signals correlated in a constant way. If science can detect pulsar signals to within a tenth of a nanosecond variations they could detect a passing gravity wave that have frequencies of nano- hertz, , 10^-9 cycles per second. Equivalent to wavelengths in years.
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- These gravity wavelengths are 10^15 times longer than AM radio wavelengths.
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- See Reviews on LIGO, Laser Interferometer Gravitational Wave Observatory, to learn more about how these long gravity waves might be detected.
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- Once science is able to detect gravitational waves they hope to study fundamental interactions of particles at energy levels far greater than our Earthly Particle Accelerators can produce today. Energy levels present after the Big Bang and during the period of Cosmic Inflation.
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- There is much more to learn, it is a big Universe out there, how big? Stay tuned.
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RSVP, with comments, suggestions, corrections. Index of reviews available ---
--- Some reviews are at: -------------------- http://jdetrick.blogspot.com -----
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