- 3989 - UNIVERSE - how big is it? Planck’s satellite findings were published in 2015. By carefully examining the microwave background radiation, astronomers have pinned down the universe’s age to 13.8 billion years, accurate to better than 1 percent. And that is how big it is too, in lightyears.
– -------------------------- 3989 - UNIVERSE - how big is it?
- With a long enough
lever and a place to stand, Archimedes knew he could move the Earth. Where
could he stand to weigh the Universe?
When it comes to imagining such colossal masses, the human mind is
completely out of its depth.
-
- But first, a note
about weight and mass—intimately related but technically distinct qualities.
Officially, “weight” describes the gravitational force acting on an object, so
an a galaxy “weighs” nothing while floating in empty space.
-
- What researchers
are really after is mass, the unvarying amount of stuff in an object, or
equivalently, how much force it takes to get the mass moving. “Weighing” an object comes down to measuring the gravitational
force between it and a massive partner.
-
- Early attempts to
weigh the Earth went the route of guessing the planet’s size and density and
calculating its mass from there. By the 1600s, estimates of Earth’s diameter,
and therefore its volume , were made . But no one was sure of the density,
whether the planet was made of mostly water or rock. Everyone was wrong at the
time because the planet is actually made up mostly of metal, which is denser
than both.
-
- To figure out that
density and therefore the mass of the Earth, British scientist Henry Cavendish
measured the overall strength of gravity in 1798. Isaac Newton had shown in the
1600s that all objects pull on all other objects, and those with more mass pull
harder.
-
- Cavendish hung
small metal balls from a wire, placed heavier spheres nearby, and watched the
wire twist as the spheres attracted each other. In this horizontal twisting he
was able to determine the intensity of the gravitational force between the
weights and in general.
-
- Knowing how hard the Earth’s mass tugged downward on his
spheres (that is, their weights), he could use Newton’s equations to peg the
Earth’s composition at a suspiciously metal-like 5.42 times the density of
water. Modern physicists have found that he was off by just seven-tenths of one
percent.
-
- The Sun pulls on
the Earth just hard enough to swing it around once every 365 days, implying a
certain force, and therefore a certain mass. Similarly, by considering the Sun
as the prime partner of various heavenly body pairings, researchers could
calculate the mass of the rest of the planets based on the length of their
years.
-
- Watching how moons
orbited planets provided another check, as well as a way to weigh the moons.
However, asteroid mass estimation remains something of a dark art based on
guessing plausible densities and sizes.
-
- Just as researchers
can infer the mass of the Earth by watching how hard it drags down objects on
or near its surface, or the mass of the Sun by watching how quickly planets
orbit around it, they can read the “galaxy’s mass” in the motion of the objects
that circle it.
-
- It was the
trajectories of orbiting stars that first flagged the presence of dark matter
in the 1970s.
-
- In our solar
system, Mercury zips around nearly nine times faster than Neptune does because
it lies much closer to the source of the vast majority of our solar system’s
mass, the Sun.
-
- Researchers expected
that a similar pattern should play out in other galaxies, far-out stars tracing
slower orbits than close-in ones. This
relationship holds close to the center of most galaxies, but then stops. After
a point, no matter how far out they looked, astronomers discovered that stars
orbited at surprisingly similar speeds.
Their constant motions imply that a second, invisible source of mass is
also pulling on them.
-
- The Universe, inconveniently, lacks visible orbiting
partners. Here, the standard gravitational scale breaks down. The absolute size of the universe is unknown,
and is constantly expanding, so its mass is similarly undefined. Astronomers
can define the volume of the observable universe, however, based on the
distance light has been able to travel between the Big Bang and present day.
-
- But the density,
averaged out over all of the cosmos’s planets, stars, galaxies, and voids, has
proved challenging to measure. One estimate came from the Wilkinson Microwave
Anisotropy Probe (WMAP), a satellite that measured warm spots and cool spots in
the universe’s earliest light from 2001 to 2010.
-
- These warm patches are the remnants of a power struggle
from when a dense soup of matter and light filled the young universe. Gravity
drew particles together while light pushed them apart, creating sloshing
ripples that grew with the expanding universe until WMAP picked them up.
-
- From the patterns
in these variations, cosmologists can calculate the age and composition of the
universe, including its overall density.
Density works out to be about six protons worth of stuff per cubic
meter. That number technically
represents an energy density (since matter and energy can be converted using
Einstein’s famous equation), so it includes visible matter, dark matter, and
the unknown dark energy driving the expansion of the universe.
-
- WMAP and its
successor, the Planck satellite, estimated that by this metric the universe is
about 5 percent visible matter, 27 percent dark matter, and 68 percent dark
energy.
-
- The volume and
density estimates for the universe’s
overall mass as something like
100,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
kilograms. That’s roughly 100 billion Milky Way galaxies.
-
- Our deepest
astrophotos show ultra-distant quasars and galaxies whose redshifts indicate
their light has traveled for nearly 13 billion years. Thus, they are 13 billion
light-years away? And, that must define the edge of the visible universe,
right?
-
- Ever since a given
galaxy emitted the light we’re now seeing, it’s been zooming away from us due
to expanding space. Today that same galaxy is 46 billion light-years distant.
-
- How could anything
reach a distance of 46 billion light-years in the mere 13 billion years since
it emitted the light we now see? That would mean it’s currently receding faster
than light. Or that space is so warped we’re not viewing it directly.
-
- Actually, both are
true. Faster-than-light recession doesn’t violate relativity in this case
because the galaxy’s mass was never accelerated. It’s merely the intervening
empty space between galaxies that has been inflating, which makes the real
radius of the observable universe very nearly 46 billion light-years.
-
- Light from objects
any farther away will never get here because space’s expansion will stretch
out, hopelessly weaken, and out-race their rays. So, it’s a real boundary
beyond which there is eternal blankness. We use the term visible universe for
everything nearer, which is everything we can ever possibly know about.
-
- Given the average
density of space, five atoms per cubic yard (1 cubic meter), the visible
universe must contain 10^56 tons of matter. And 10^84 photons of light.
-
- What about the
universe beyond the part we can see? The real universe? How big is the whole
thing?
-
- One theory, using
the most plausible figures for when the era of inflation began just after the
Big Bang, concludes that the overall universe is 300 billion trillion times
larger than the visible universe.
-
- Let’s try another
avenue to calculate the size of the Universe?
The “fine structure constant” seems annoyingly inconstant at the outer
fringes of the unvierse , it occurs in only one direction that we look. The ‘fine structure constant’ is a measure of
electromagnetism, one of the four fundamental forces in nature (the others are
gravity, weak nuclear force and strong nuclear force).
-
- The fine structure
constant is the quantity that physicists use as a measure of the strength of
the electromagnetic force
-
----------------------------
Find Structure Constant = e^2
/ h * c
-
----------------------------
Find Structure Constant = 1
/ 137
-
- It's a
dimensionless number and it involves the speed of light, “c”, something called
Planck's constant, “h”, and the electron
charge , “e“, and it's a ratio of those things. And it's the number that
physicists use to measure the strength of the electromagnetic force.
-
- The electromagnetic
force keeps electrons whizzing around a nucleus in every atom of the universe,
without it, all matter would fly apart. It is believed to be an unchanging
force throughout time and space.
-
- The most distant
quasars that we know of are about 12 to 13 billion light years from us.
–
-
- If you can study
the light in detail from distant quasars, you're studying the properties of the
universe as it was when it was in its infancy, only a billion years old.
-
- The universe then
was very, very different. No galaxies existed, the early stars had formed but there
was certainly not the same population of stars that we see today. And there
were no planets.
-
- The universe may
not be isotropic in its laws of physics—one that is the same, statistically, in
all directions. But in fact, there could be some direction or preferred
direction in the universe where the laws of physics change, but not in the
perpendicular direction. In other words, the universe in some sense, has a
dipole structure to it.
-
- In one particular
direction, we can look back 12 billion light years and measure electromagnetism
when the universe was very young. Putting all the data together,
electromagnetism seems to gradually increase the further we look, while towards
the opposite direction, it gradually decreases.
-
- In other directions
in the cosmos, the fine structure constant remains just that—constant. These
new very distant measurements have pushed our observations further than has
ever been reached before.
-
- In other words, in
what was thought to be an arbitrarily random spread of galaxies, quasars, black
holes, stars, gas clouds and planets, with life flourishing in at least one
tiny niche of it, the universe suddenly appears to have the equivalent of a
north and a south.
-
- For a long time, it
has been thought that the laws of nature appear perfectly tuned to set the
conditions for life to flourish. The strength of the it may be the oldest
question in astronomy: How big is the universe?
-
- Faster-than-light
recession doesn’t violate relativity in this case because the galaxy’s mass was
never accelerated. It’s merely the intervening empty space between galaxies
that has been wildly inflating, which makes the real radius of the observable
universe very nearly 46 billion light-years.
-
- Light from objects
any farther away will never get here because space’s expansion will stretch
out, weaken, and out-race their rays.
So, it’s a real boundary beyond which there is eternal blankness. We use the
term visible universe for everything nearer, which is everything we can ever
possibly know about.
-
- There’s no sign
that galaxy clusters get any sparser as we approach the edge of the observable
universe. One theory, using the most
plausible figures for when the era of inflation began just after the Big Bang,
concludes that the “overall universe” is 300 billion trillion times larger than
the “visible universe“.
-
- Where the
fundamental physical quantities like the fine structure constant are 'just
right' to favor our existence, apply throughout the entire universe?
-
- Our standard model
of cosmology is based on an isotropic universe, one that is the same,
statistically, in all directions. When astronomers consider the universe at the
largest scales, they assume that it's homogeneous, and isotropic.
-
- “Homogeneous“
means that observers in any part of the universe will see roughly the same view
as observers in any other part.
-
- “Isotropic means”
that the universe looks the same in every direction. If you were floating alone
in the cosmic void, you could look left, right, up, down out to the edge of the
observable universe and see galaxies, galaxy clusters and eventually the cosmic
microwave background radiation in all directions. Every direction looks the
same.
-
- This is know as the
“cosmological principle“, and it's one of the foundations of astronomy, because
it means that we have a chance at understanding the physical laws of the
universe.
-
- If the universe
wasn't homogeneous and isotropic, then it would mean that the physical laws as
we understand them are impossible to comprehend. Just over the cosmological
horizon, the force of gravity might act in reverse, the speed of light might be
slower than walking speed, and unicorns could be real.
-
- While we don't live
in a special place in the universe, we do live in a special time in the
universe. In the distant future, billions or even trillions of years from now,
galaxies will be flying away from us so quickly that their light will never
reach us. The cosmic background microwave radiation will be redshifted so far
that it is completely undetectable.
-
- Future astronomers
will have no idea that there was ever a greater cosmology beyond the Milky Way
itself. The evidence of the Big Bang and the ongoing expansion of the universe
will be lost forever. If we didn't
happen to live when we do now, within only billions of years of the beginning
of the universe, we'd never know the truth.
-
- Using today’s most powerful telescopes, astronomers see
galaxies located over 13 billion light-years from Earth. (A light-year equals about 6 trillion
miles.) Since they see these distant galaxies in all directions, the current
“horizon” of visibility is at least 26 billion light-years in diameter.
-
- But the universe is
probably much larger than the portion we can see. This will be the case in the
highly likely event that the inflation hypothesis, put forth in 1980 by MIT’s
Alan Guth, proves correct. This idea suggests that the extremely young universe
experienced a brief period of hypergrowth so severe that it ballooned from the
size of a subatomic particle to the size of a softball almost instantly.
-
- If inflation
occurred, then the universe is much larger than we might expect based on
current observations. For now, it’s
wondrous enough to know we live in a universe that’s at least 550 billion
trillion miles across, and it may be much bigger than that
-
- The launch of
NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) in 2001 and the European
Space Agency’s Planck satellite in 2009 changed all that. Before WMAP and Planck, the best approach
for determining the universe’s age relied on the much-debated Hubble constant,
a figure that describes the rate at which the universe is expanding.
-
- To find the Hubble
constant, astronomers observe distant galaxies and measure their distances (by
using Cepheid variable stars or other objects of known intrinsic brightness) as
well as how fast they recede from Earth. They then determine the Hubble
constant by dividing the galaxy’s speed of recession by its distance.
-
- Once they decide on a value for the Hubble constant, they
can estimate the maximum age of the universe by calculating the constant’s
reciprocal.
-
- But there was a
problem. The values astronomers got for the Hubble constant depended on various
assumptions about the universe’s density and composition and the method used to
determine distances. So astronomers of different mindsets got different values
for the constant.
-
- They generally
divided into two camps, one in the range of 50 kilometers per second per
megaparsec and the other up at 80 km/sec/Mpc. (A megaparsec equals 3.26 million
light-years, or about 20 billion billion miles.)
-
- Therefore, the two
groups estimated a range for the age of the universe of about 10 to 16 billion
years. (Higher values of the Hubble constant produce younger age values for the
universe.) Let’s settle on 76
km/sec/Mpc.
-
- Researchers
announced Planck’s findings in 2015. By carefully examining the microwave
background radiation, astronomers have pinned down the universe’s age to 13.8
billion years, accurate to better than 1 percent. And that is how big it is too, in
lightyears. So, now you know.
-
May
7, 2023 UNIVERSE - how
big is it? 2813 3989
--------------------------------------------------------------------------------------------- Comments appreciated and Pass it on to
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“Jim Detrick”
--------------------------------
--------------------------- --- Sunday, May 7, 2023
---------------------------
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