- 3439 - UNIVERSE - Expanding in all directions. - Earth’s motion through space isn’t just defined by our axial rotation or our motion around the Sun, but the Solar System’s motion through the galaxy, the Milky Way’s motion through the Local Group, and the Local Group’s motion through intergalactic space.
------------- 3439 - UNIVERSE - Expanding in all directions.
- Only with all the motions combined, and by comparing to the Big Bang’s leftover glow, can we arrive at a meaningful answer of how the Earth and you are moving through the Universe.
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- The Earth spins on its axis, orbits the Sun, and travels through the Milky Way, which itself is in motion relative to all the other galaxies around us. By measuring the objects around us and the light left over from the Big Bang, maybe we can determine our cumulative cosmic motion.
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- The Earth rotates on its axis, spinning a full 360° with each passing day. You are moving east at 700 miles per hour. The pendulum takes two full rotations of Earth in order to make a single, complete rotation at this particular latitude; the rotation angle, just like the speed at Earth’s surface, is latitude-dependent
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- That translates into an equatorial speed of 1000 miles / hour, dropping lower with increasing latitudes. At my latitude it is down to 700 miles per hour. At the north pole you just turn in little circles.
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- The Earth, moving in its orbit around the Sun and spinning on its axis, appears to make a closed, unchanging, elliptical orbit. Our planet is actually spiraling away from the Sun by about 1.5 centimeters per year, and “precesses” in its orbit on timescales of tens of thousands of years.
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- Meanwhile, the Earth revolves around the Sun, at speeds ranging from 67,000 miles per hour.
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- Just 800 years ago, perihelion and the winter solstice aligned. Due to the precession of Earth’s orbit, they are slowly drifting apart, completing a full cycle every 21,000 years. Over time, the Earth drifts slightly farther from the Sun, the precession period increases, and the eccentricity varies as well.
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- Early January’s perihelion causes the fastest motions, while July’s aphelion yields the slowest.
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- All of the major planets orbit the Sun in ellipses that are nearly circles, with only a few percent deviation among even the most eccentric planets. The rotational speed of any planet is tiny compared to its orbital speed, but the orbital speeds of the planets are small compared to the Solar System’s motion through the galaxy.
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- The entire Solar System travels around the Milky Way. The Sun, like all the stars in our galaxy, orbits around the galactic center at speeds of thousands of miles per second. In our neighborhood, the speed of the Sun and the other stars around the galactic center have an uncertainty of around 10%, on 44,739 mph, which is the largest factor of uncertainty when it comes to calculating our cumulative motion.
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- Our heliocentric speed of 469,757 mph is inclined 60° to the plane of the planets.
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- Although the Sun orbits within the plane of the Milky Way some 25,000 to 27,000 light years from the center, the orbital directions of the planets in our Solar System do not align with the galaxy at all.
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- The orbital planes of the planets occur randomly within a stellar system, often aligned with the central star’s rotational plane but randomly aligned with the plane of the Milky Way.
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- However, our motion isn’t vortical, but a simple sum of these velocities. Vortical means whirling around a vortex. An accurate model of how the planets orbit the Sun, which then moves through the galaxy in a different direction-of-motion.
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- The speeds of the planets around the Sun are only a small fraction of the Solar System’s motion through the Milky Way galaxy, with even Mercury’s revolution around the Sun contributing only 20% of its total motion through our galaxy.
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- The Milky Way and Andromeda travel toward each other at 244,000 miles per hour. When two galaxies merge, their supermassive blackholes are fully expected to merge together as well.
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- Attractive clumps and repulsive underdense regions both tug on our Local Group of Galaxies. The Virgo supercluster, spans more than 100 million light-years and contains our Local Group, which has the Milky Way, Andromeda, Triangulum, and about 60 smaller galaxies. The overdense regions gravitationally attract us, while the regions of below-average density effectively repel us relative to the average cosmic attraction.
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- Combined, we move 1,402,560 miles per hour relative to the cosmic average.
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- Because matter is distributed roughly uniformly throughout the Universe, it isn’t just the overdense regions that gravitationally influence our motions, but the underdense regions as well. A feature known as the “dipole repeller” was discovered only recently, and may explain our Local Group’s peculiar motion relative to the other objects in the Universe.
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- However, the Big Bang’s leftover photons offer a cosmically unique rest frame. At any epoch in our cosmic history, any observer will experience a uniform “bath” of Omni-directional radiation that originated back at the Big Bang. Today, from our perspective, it’s just 2.725 K above absolute zero, and hence is observed as the “cosmic microwave background“, peaking in microwave frequencies.
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- The Sun moves at a cumulative 823,200 mph relative to the Cosmic Microwave Background (CMB). Although the cosmic microwave background is the same rough temperature in all directions, there are 1-part-in-800 deviations in one particular direction: consistent with this being our motion through the Universe.
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- At 1-part-in-800 the overall magnitude of the CMB’s amplitude itself, this corresponds to a motion of about 1-part-in-800 the speed of light, or 823,200 mph.
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- An inherent uncertainty of ± 4,500 mph comes from not knowing the intrinsic CMB dipole’s magnitude.
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- Although we can measure the temperature variations all across the sky, on all angular scales, we cannot disentangle whatever the intrinsic dipole in the cosmic microwave background is, as the dipole we observe, from our motion through the Universe, is more than a factor of 100 larger than whatever the primordial value is.
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- With only one location to measure the value of this parameter , we cannot disentangle which part is due to our motion and which part is inherent; it would take tens of thousands of such measurements to reduce the uncertainties here below their current values. Being confined to the Milky Way, we can only dream of making such measurements.
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- The initial fluctuations that were imprinted on our observable universe during inflation may only come into play at the 0.003% level, but those tiny imperfections lead to the temperature and density fluctuations that appear in the cosmic microwave background and that seed the large-scale structure that exists today.
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- Measuring the CMB at a variety of cosmic locations would be the only feasible way to disentangle the intrinsic dipole of the CMB from that induced by our motion through the Universe.
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- One hundred years ago, a Russian cosmologist named Alexander Friedmann proposed the idea that the Universe expands from a singular point. A true visionary, he also found that the Universe could oscillate in time, with alternating periods of expansion and contraction. We now call the equations that describe the temporal evolution of the Universe the “Friedmann equations.”
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- The expansion of the Universe is one of the most remarkable scientific findings of all time. It is also widely misunderstood, both conceptually and historically.
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- Expansion is not like a bomb. Expansion means cooling. When we say the universe is “expanding,” it is hard to avoid the image of a bomb that detonated a long time ago. The Big Bang is the “explosion,” and the galaxies that fly away from the exploding point are like shrapnel spreading outward in all directions from that central point.
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- But that is not what the cosmic expansion means at all. If this image was accurate, space would be a static background, and the Universe would have a very special point, the center where the explosion originated. But there is no special point in the Universe. Cosmic geometry is very democratic, with all points being equal in the eyes of space.
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- The usual way this is explained is by picturing a balloon with coins glued to its surface. The balloon’s surface represents space (in two dimensions, which is easier to see), and the coins represent galaxies.
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- As the balloon expands, the coins stay the same size but move away from one another. If you were a being in one galaxy, you would see all other galaxies moving away from you. But so would your neighbors as well as observers in any of the other galaxies.
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- This is what is meant by the Universe not having a center. All points on the balloon are stretching away from one another. The expansion of space carries the galaxies (coins) away.
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- This is an example of an expanding “closed” geometry, since the surface of the balloon is closed: if you start moving in one direction, you would get back to your starting point.
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- Now play the movie backward for both examples. The balloon shrinks, the classroom shrinks. At some moment in the past, all the coins and desks would be on top of one another, a big bundle of stuff. That is the point of maximum compression that, extrapolated to its ultimate mathematical limit, would be a point of infinite mass-energy density.
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- In 1917, Einstein found the first solution for the geometry of the Universe, using his brand new theory of general relativity, the theory that attributes gravity to the curvature of space around a massive body. Einstein’s result was quickly followed by another solution by the Dutch Willem de Sitter, also from 1917.
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- Einstein’s solution pictured a static spherical universe with radius and a “cosmological constant,” a parameter he put in by hand to find a static solution. How remarkable is it that with paper and pen in hand a human could devise a theory for the Universe as a whole?
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- De Sitter’s solution was different. His universe was empty, that is, it had no matter, only the cosmological constant. It was later shown that de Sitter’s solution was equivalent to a Universe filled with the cosmological constant expanding exponentially fast. This was of interest because observations were showing that the light from distant “nebulae” (later shown to be galaxies) was redshifted, stretched toward the red end of the color spectrum (which goes from violet to red, like the rainbow).
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- De Sitter and others suggested that this redshift was possibly due to the moving of the nebulae away from us, like the Doppler shift from car horns that change as they move away (lower pitch) or approach (higher pitch).
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- The Friedmann equations dated June 29, 1922, discovers that one doesn’t need either to impose a static Universe (Einstein) or an empty one (de Sitter) to find solutions with expanding geometry.
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- So, he takes the radius to change in time, and solves for R(t), with the time variable denoting “the time that passed since Creation”. Friedmann discovered different solutions that depend on the relative value of the cosmological constant and other parameters.
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- In the “Monotone World of the First Kind,” the Universe starts at a singularity at t =0 and expands in a rate that first decelerates and then accelerates in time forever.
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- In the “Monotone World of the Second Kind,” expansion starts from a finite radius and goes on exponentially fast forever.
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- Friedmann found what he called the “Periodic World,” where the Universe starts from a singularity at t = 0 and expands and contracts periodically in time.
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- In 1923, Friedmann published his book “World as Space and Time“, where he makes a connection between his periodic Universe and Hindu mythology, while making an estimate for the age of the Universe expanding from “nothingness”.
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- A non-static Universe represents a variety of cases. It is possible that the radius of curvature constantly increases from a certain initial value; it is also possible that the radius changes periodically. The Universe compresses into a point (into nothingness), then increases its radius to a certain value, and then again compresses into a point.
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- In 1929, Edwin Hubble confirmed Vesto Slipher’s previous data on receding nebulae, since then correctly understood as galaxies in an expanding universe. We now call the cosmological constant, or something very similar to it, “dark energy.”
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February 1, 2022 UNIVERSE - Expanding in all directions. 3422
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