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---------------------------------- 2404 - SPACE - vacuum of space?
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- What is in the Vacuum of Space? To create a vacuum we take a known volume, say a glass jar, and pump all the atoms out of the jar. What is left is a vacuum. However, those atoms are hard to remove.
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- The best vacuum we can create here on Earth still contains about 1,000,000,000,000 atoms per cubic meter, 10^12 atoms/m^3. The average density of the Sun is 10^30 atoms per cubic meter. The average density of our Galaxy is 10^6 atoms per cubic meter. The average density of our Universe is 1 atom per cubic meter. That is about as close to pure vacuum as you are going to get. But, what is left? Is it truly empty space?
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- There still is energy in empty space. The average density of photons in the Universe is 10^9 per cubic meter. So, for every atom there is 1,000,000,000 photons in the Universe. The energy in space that we measure as the Cosmic Microwave Background Radiation is at a temperature of 2.7 degrees Kelvin.
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- This means that there are 411,000,000 photons per cubic meter in the Cosmic Microwave Background. We can say that most of our Universe is a vacuum of a little mass and a little more energy. To understand this vacuum we have to go back to Einstein’s equations of Relativity
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- Einstein abandoned the idea that motion was absolute. He concluded that all motion was relative. If that were true, then change in space / change in time, which defines motion, or velocity, is also relative.
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- But, for light to remain constant for all observers, the change in space / change in time must be adjusted according to the observer’s relative motion. Making these adjustments Einstein derived all new laws for space, mass, energy and time. Space is also length and distance, and mass is also energy. So, his new laws affected almost everything.
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- Einstein’s new laws of motion reduce to be the same as Newton’s laws of motion at slower velocities. But, as the velocities approach the speed of light in empty space the equations of Relativity must be used.
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- It remains to be seen but Einstein’s laws may also be limited to cases of low energy. A far deeper and wider set of equations may be needed for the highest energies. However, these new equations have yet to be discovered.
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- Newton’s laws were simple, that the force of gravity between two masses falls off in proportion to the square of the distance between them. Einstein’s laws are complicated field equations.
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- His laws state that the presence of mass and energy curve space and slow time. Bodies in motion in curved space-time simply take the quickest path. Much like an airplane flying from Chicago to London takes a Great Circle route over the polar region to get the fastest transit time over the curved surface of Earth.
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- The complexity comes in when every solution to Einstein’s field equations describes an entirely different Universe. Each solution depends on the distribution of matter-energy and the space-time geometry in which it lies. We do not know which solution matches exactly the Universe we are trying to observe. Each field equation is extremely difficult to solve.
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- To simplify them as much as possible three assumptions are often made. That the Universe is homogenous - the density of matter is the same everywhere, and the Universe is isotropic - the density of matter is the same in every direction, and the Universe is Static - the density of matter is unchanging over time.
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- There is one more complication in Einstein’s field equations - gravity acts upon itself. Gravity interacts with itself in a way that light does not. As gravity waves spread out, rippling the curvature of space-time, carrying energy, that energy acts as a source for its own gravitational field.
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- Science has just began to detect these gravity waves that are traveling at the speed of light. We are using new (LIGO) instruments to detect them and we know they exist by observing their effect on binary stars.
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- After years of observing binary neutron stars (pulsars) spiraling in toward each other, we measure the slowing or decaying of their orbits to exactly match the rate predicted if gravity waves were radiating away carrying energy.
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- Gravity waves are not waves in the traditional sense they are more like a traveling geometry of space and time.
- If we make the conclusion that the Universe is homogeneous and isotropic it turns out that it can not be static. The equations require that either has to be expanding or contracting. If it were static gravity would over time contract the Universe and matter would pile up in a cosmic implosion.
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- Hubble’s evidence showed the Universe was expanding and Einstein had to add a constant to his equations to account for an expanding Universe. His equations had the form:
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--------------------- Geometry of space-time = distribution of mass-energy.
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- In order to maintain a conservation of energy and momentum in his equations he had to add a force between all the masses that increased in proportion to the distance between them.
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-------------- Geometry of space-time + Unknown Force = distribution of mass-energy
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- If this force is positive it is a repulsive force counteracting gravity which would be an opposite attractive force. This would create a steady-state or static Universe. It would cause distant masses to repel one another. The force would not be noticed on Earth because the force increases with distance and only becomes effective at astronomical dimensions.
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- If the force value was chosen just right it would exactly counter balance the gravitational attractive inverse square law. The force could be positive or negative allowing a static Universe, an expanding Universe, or a Collapsing Universe.
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- As mentioned earlier starting in 1965 evidence was accepted that the Universe is expanding. By 2006 astronomers had found that Type 1A Supernova with known intrinsic brightness to have an apparent brightness 9 times fainter, or 3 times further distant than expected. This evidence along with the Cosmic Background Radiation has convinced astronomers not only is the Universe expanding it is accelerating in its expansion.
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- The unknown force became known as the Cosmological Constant, and later Dark Energy, or vacuum energy. To try to understand this vacuum energy astronomers have had to learn particle physics and quantum mechanics.
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- A great frustration quickly set in. Einstein’s equations do not work at quantum dimensions. Infinities turn up in the equations that can not be resolved. Quantum Mechanics equations work well.
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- In the quantum world energy is quantified by Max Planck’s Constant of Action and all particles behave both as point particles and as waves. Quantum bundles of energy were necessary to explain the black body curve and the light curves of supernova.
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- The black body curve is the spectrum of energy versus wavelength and the temperature of a radiating body. It always has the same shape. The Cosmic Background Radiation fit’s the black body curve exactly at a temperature of 2.73 Kelvin.
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- Somehow the vacuum fluctuations in space are the source of the Dark Energy that is expanding the Universe at an every faster rate. The cosmic vacuum can be viewed as a sea of elementary particles and their anti-particles that are continually appearing and disappearing, annihilating each other according to E=mc^2. But, their lifetimes are so short as to never exceed Planck’s Uncertainty limit of Planck’s constant/2*pi.
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- The uncertainty of energy * the uncertainty in lifetime is always greater than Planck’s Constant/ 2*pi. Planck’s Constant = 6.625*10^-34 kilogram * meters^2/second. This is called the Werner Heisenberg Uncertainty Principle. It certainly applies to the vacuum of space because a lot is uncertain and remains to be discovered.
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- Other Reviews available to learn more:
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- 2243 - What is space really?
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- 2074 - Space is much todo about nothing. There is much more nothing in his world than there is something.
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- 2049 - The expanding universe?
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- 2019 - You need to expand your mind to keep up with astronomy.
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- 1831 - From blackholes to empty space?
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- 1773 - Space is what separates things?
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- 1407 - Space is in constant motion? It is anything but empty.
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- 1241 - At the smallest level things remain connected even though they are separated in space?
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- June 22, 2019 660
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--------------------- June 22, 2019 --------------------
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