- 4315 - DARK ENERGY MYSTERY ? - Over ten years ago, the Dark Energy Survey (DES) began mapping the universe to find evidence that could help us understand the nature of the mysterious phenomenon known as “dark energy”.
------------------------- 4315 - DARK ENERGY MYSTERY ?
- Dark energy is
estimated to make up nearly 70% of the observable universe, yet we still don't
understand what it is. While its nature remains mysterious, the impact of dark
energy is felt on grand scales. Its primary effect is to drive the accelerating
expansion of the universe.
-
- The Universe is
expanding at 49,300 miles per hour for
every 1 million lightyears distance.
-
- The “cosmological
constant” that was introduced by Albert Einstein in 1917 as a way of
counteracting the effects of gravity in his equations to achieve a universe
that was neither expanding nor contracting. Einstein later removed it from his
calculations. The Universe was
expanding.
-
- Cosmologists later
discovered that not only was the universe expanding, but the expansion was
accelerating. This observation was attributed to the mysterious quantity called
dark energy. Einstein's concept of the cosmological constant could actually
explain “dark energy”. If it had a
positive value it was allowing it to conform to the accelerating expansion of
the universe.
-
- The DES results are
the culmination of decades of work by researchers around the globe and provide
one of the best measurements yet of an elusive parameter called "w",
which stands for the "equation of state" of dark energy. Since the
discovery of dark energy in 1998, the value of its equation of state has been a
fundamental question.
-
- This “state”
describes the ratio of pressure over energy density for a substance. Everything
in the universe has an equation of state.
Its value tells you whether a substance is gas-like, relativistic
(described by Einstein's theory of relativity) or not, or if it behaves like a
fluid. Working out this figure is the first step to really understanding the
true nature of dark energy.
-
- Our best theory
for “w” predicts that it should be exactly minus one (w = -1). This prediction also assumes that dark
energy is the cosmological constant proposed by Einstein. An equation of state of minus one tells us
that as the energy density of dark energy increases, so the negative pressure
also increases.
-
- The more energy
density in the universe, the more repulsion there is, matter pushes against
other matter. This leads to an ever-expanding accelerating universe. It might
sound a bit bizarre, as it is counter-intuitive to everything we experience on
Earth.
-
- The work uses the
most direct probe we have on the expansion history of the universe: Type Ia
supernovae. These are a type of star explosion and they act as a kind of cosmic
yardstick, or standard candle, allowing us to measure staggeringly large
distances far into the universe. These distances can then be compared to our
expectations. This is the same technique that was used to detect the existence
of dark energy 25 years ago.
-
- The difference now
is in the size and quality of our sample of supernovae. Using new techniques,
the DES team has 20 times more data, over a wide range of distances. This
allows for one of the most precise ever measurements of “w”, giving a value of
-0.8
-
- At first sight,
this is not the precise minus one value that we predicted. This might indicate
that it is not the cosmological constant. However, the uncertainty on this
measurement is large enough to allow minus one at a 5% chance, or betting odds
of only 20 to 1. This level of uncertainty is not good enough yet to say either
way, but it's an excellent start.
-
- The detection of
the Higgs Boson subatomic particle in 2012 at the Large Hadron Collider
required odds of a million to one chance of being wrong. However, this
measurement may signal the end of "Big Rip" models which have
equations of state that are more negative than one. In such models the universe
would expand indefinitely at a faster and faster rate, eventually pulling apart
galaxies, planetary systems and even space-time itself.
-
- Scientists want
more data and those plans are already well underway. The DES results suggest
that our new techniques will work for future supernova experiments with ESA's
“Euclid mission” (launched July 2023) and the new “Vera Rubin Observatory” in
Chile. This observatory should soon use its telescope to take a first image of
the sky following construction, giving a glimpse into its capabilities.
-
- These
next-generation telescopes could find thousands more supernovae, helping us
make new measurements of the equation of state and shedding even more light on
the nature of dark energy. Hang in
there, we arn't done yet.
-
-
January 12, 2023
- DARK
ENERGY MYSTERY ? 4315
------------------------------------------------------------------------------------------
-------- Comments
appreciated and Pass it on to whomever is interested. ---
--- Some reviews are
at: -------------- http://jdetrick.blogspot.com -----
-- email feedback,
corrections, request for copies or Index of all reviews
--- to: ------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
--------------------- ---
Friday, January 12, 2024 ---------------------------------
No comments:
Post a Comment