- 4030 - UNIVERSE - the shape of the Universe? - If you could somehow manage to step outside of the universe, what would it look like? Scientists have struggled with this question, taking several different measurements in order to determine the geometry of the cosmos and whether or not it will come to an end. How do they measure the shape of the universe? And what have they found?
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4030 - UNIVERSE
- the shape of the Universe?
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- What is ythe
geometry of the geometry of the universe?
According to Einstein's theory of General Relativity, space itself can
be curved by mass. As a result, the density of the universe,that is how much
mass it has spread over its volume, determines its shape, as well as its
future.
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- Scientists have
calculated the "critical density" of the universe. The critical
density is proportional to the square of the Hubble constant, which is used in
measuring the expansion rate of the universe. Comparing the critical density to
the actual density can help scientists to understand the shape.
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- If the actual
density of the universe is less than the critical density, then there is not
enough matter to stop the expansion of the universe, and it will expand
forever. The resulting shape is curved like the surface of a saddle. This is
known as an “open universe”.
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- The shape of the
universe depends on its density. If the density is more than the “critical
density”, the universe is closed and curves like a sphere; if less, it will
curve like a saddle. But if the actual density of the universe is equal to the
critical density, as scientists think it is, then it will extend forever like a
flat piece of paper.
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- The shape of the
universe depends on its density. If the density is more than the critical
density, the universe is closed and curves like a sphere; if less, it will
curve like a saddle. But if the actual density of the universe is equal to the
critical density, as scientists think it is, then it will extend forever like a
flat piece of paper.
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- If the actual
density of the universe is greater than the critical density, then it contains
enough mass to eventually stop its expansion. In this case, the universe is
closed and finite, though it has no end, and has a “spherical shape”.
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- Once the universe
stops expanding, it will begin to contract. Galaxies will stop receding and
start moving closer and closer together. Eventually, the universe will undergo
the opposite of the Big Bang, often called the "Big Crunch." This is
a” closed universe”.
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- However, if the
universe contains exactly enough mass to eventually stop the expansion, the
actual density of the universe will equal the critical density. The expansion
rate will slow down gradually, over an infinite amount of time. In such a case,
the universe is considered “flat and infinite in size”.
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- Measurements
indicate that the universe is flat, suggesting that it is also infinite in
size. The speed of light limits us to viewing the volume of the universe
visible since the Big Bang; because the universe is approximately 13.8 billion
years old, scientists can only see 13.8 billion light-years from Earth.
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- While studying
distant galaxies in the early 20th century, astronomer Edwin Hubble realized
that they all seemed to be rushing away from the Milky Way. He announced that
the universe was expanding in all directions. Since then, astronomers have
relied on measurements of supernova and other objects to refine his calculations
of how quickly the universe is expanding.
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- Incomprehensible
as it sound, inflation poses that the universe initially expanded far faster
than the speed of light and grew from a subatomic size to a golf-ball size
almost instantaneously.
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- Other instruments
measure the background radiation of the universe in an effort to determine its
shape. NASA's Wilkinson Microwave Anisotropy Probe (WMAP) measured background
fluctuations in an effort to determine whether the universe is open or closed.
In 2013, scientists announced that the universe was known to be flat with only
a 0.4 percent margin of error.
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- Physicists may
have solved a decades-long mystery about how our universe came to be. There's a hole in the story of how our
universe came to be. First, the universe inflated rapidly, like a balloon.
Then, everything went boom. But, how those two periods are connected has
eluded physicists. Now, a new study suggests a way to link the two epochs.
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- In the first
period, the universe grew from an almost
infinitely small point to nearly an octillion (that's a 1 followed by 27 zeros)
times that in size in less than a trillionth of a second. This inflation period
was followed by a more gradual, but violent, period of expansion we know as the
Big Bang.
- During the Big
Bang, an incredibly hot fireball of fundamental particles — such as protons,
neutrons and electrons — expanded and cooled to form the atoms, stars and
galaxies we see today.
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- The Big Bang
theory, which describes cosmic inflation, remains the most widely supported
explanation of how our universe began, yet scientists are still perplexed by
how these wholly different periods of expansion are connected.
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- When the universe
expanded in a flash of a second during cosmic inflation, all the existing
matter was spread out, leaving the universe a cold and empty place, devoid of
the hot soup of particles needed to ignite the Big Bang. During the reheating
period, the energy propelling inflation is believed to decay into particles.
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- Once those
particles are produced, they bounce around and knock into each other,
transferring momentum and energy,
That's what thermalizes and reheats the universe to set the initial
conditions for the Big Bang.
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- In this model,
scientists simulated the behavior of exotic forms of matter called
“inflatons”. Scientists think these
hypothetical particles, similar in nature to the Higgs boson, created the
energy field that drove cosmic inflation. Their model showed that, under the
right conditions, the energy of the inflatons could be redistributed
efficiently to create the diversity of particles needed to reheat the universe.
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- The transition
from the cold inflationary period to the hot period is one that should hold
some key evidence as to what particles really exist at these extremely high
energies. One fundamental question
that plagues physicists is how gravity behaves at the extreme energies present
during inflation.
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- In Albert
Einstein's theory of general relativity, all matter is believed to be affected
by gravity in the same way, where the strength of gravity is constant
regardless of a particle's energy. However, because of the strange world of
quantum mechanics, scientists think that, at very high energies, matter
responds to gravity differently.
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- Putting this
assumption in the model, tweaking how
strongly the particles interacted with gravity,
they discovered that the more they increased the strength of gravity,
the more efficiently the inflatons transferred energy to produce the zoo of hot matter particles found during
the Big Bang.
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- This reheating
period should leave an imprint somewhere in the universe. Astronomers just need
to find it. But finding that imprint
could be tricky. Our earliest glimpse of the universe is a bubble of radiation
left over from a few hundred thousand years after the Big Bang, called the
cosmic microwave background (CMB). Yet the CMB only hints at the state of the
universe during those first critical seconds of birth.
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May 31, 2023
UNIVERSE - the shape of the Universe? 4030
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