- 4029 - UNIVERSE EXPANDING - how did it start? 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 unierse and whether or not it will come to an end.
------------- 4029 - UNIVERSE EXPANDING - how did it start?
- How do they
measure the shape 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, or,
how much mass it has spread over its volume, determines its shape, as
well as its future.
-
- 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 cosmos.
-
- 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”.
-
- 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.
-
- 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”.
-
- 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
known as a “closed universe”.
-
- 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.
-
- 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.
-
- 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 calculations of
how quickly the universe is expanding.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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. To solve this
cosmic mystery, a team of researchers at MIT and the Netherlands' Leiden University
simulated the critical transition between cosmic inflation and the Big Bang, a
period they call "reheating."
-
- The
post-inflation reheating period sets up the conditions for the Big Bang and, in
some sense, puts the 'bang' in the Big Bang.
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. Once those particles are
produced, they bounce around and knock into each other, transferring momentum
and energy. And, that's what thermalizes and reheats the
universe to set the initial conditions for the Big Bang.
-
- 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.
-
- 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. 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. Their model tweaked 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.
-
- Now, they need to
find evidence to buttress their model somewhere in the universe. Astronomers 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. Future observations of gravitational waves will hopefully provide the
final clues.
-
May
28, 2023 UNIVERSE EXPANDING
- how did it start?
4029
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--------------------- --- Sunday, May 28, 2023
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