- 4445
- UNIVERSE EXPANDING
- how to measure it? -
James Webb Telescope continues to confirm that the Universe is behaving
strangely? Over a century ago,
astronomers Edwin Hubble and Georges Lemaitre independently discovered that the
Universe was expanding. Since then, scientists have attempted to measure the
rate of expansion (known as the Hubble-Lemaitre Constant) to determine the
origin, age, and ultimate fate of the Universe.
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------------------------- 4445 - UNIVERSE EXPANDING - how to measure it?
- Measuring universe expansion rate has
proved very daunting, as ground-based telescopes yielded huge uncertainties,
leading to age estimates of anywhere between 10 and 20 billion years! This
disparity between these measurements, produced by different techniques, gave
rise to what is known as the “Hubble Tension”.
-
- It was hoped that the Hubble Space
Telescope (launched in 1990) would resolve this tension by providing the
deepest views of the Universe to date. After 34 years of continuous service,
Hubble has managed to shrink the level of uncertainty but not eliminate it.
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- This led some in the scientific community
to suggest that Hubble‘s measurements were incorrect. But according to the
latest data from the James Webb Space Telescope (JWST), Hubble’s successor, it
appears that the venerable space telescope’s measurements were right all along.
-
- The Hubble Tension arises from the fact
that different distance measurements ( the “Cosmic Distance Ladder“) result in
different values. For the calibration of short distances or the first “rung” on
the ladder, astronomers rely on “parallax” measurements of nearby stars.
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- For the next “rung,” they rely on “Cepheid
variables” and “Type Ia supernovae” to measure the distances to objects tens of
millions of light-years away. Distance measurements for these stars by Hubble
yielded a value of 252,000 kilometers/hour per megaparsec (Mpc).
-
- The final rung consists of using redshift
measurements of the Cosmic Microwave Background (CMB) to calibrate distances of
billions of light-years. The mapping of this background by the ESA’s Planck
satellite yielded an estimate of about 244,000 km/h per Mpc (or about 269 km/s
per light year).
-
- The simplest explanation for the discrepancy
was that Hubble‘s measurements were inaccurate, perhaps because of
uncertainties in the Cosmic Distance Ladder. Since it was launched in December
2021, the JWST has made its own measurements of Cepheid variables with its
advanced infrared optics.
-
- This has allowed astronomers to cross-check
the optical-light measurements made by Hubble.
In 2011, the Nobel Prize in
Physics and the Albert Einstein Medal for his co-discovery of the accelerating
rate of cosmic expansion led to the theory of “Dark Energy.” The team’s first
look at Webb’s observations in 2023 confirmed that Hubble’s measurements of the
expanding Universe were accurate.
-
- Their latest analysis was based on Webb’s
observations of over 1,000 Cepheids used as “anchors” in the distance ladder,
eight Type Ia supernovae, and NGC 5468 – the farthest galaxy where Cepheids
have been well measured, roughly 130 million light-years distant. These findings have erased any lingering
doubt about measurement errors:
-
- With measurement errors negated, what
remains is the real and exciting possibility that we have misunderstood the
Universe. We’ve now spanned the whole range of what Hubble observed, and we can
rule out a measurement error as the cause of the Hubble Tension with very high
confidence.
-
- These findings have eliminated any
lingering doubts that measurement inaccuracies might grow with distance. These
inaccuracies would result from “stellar crowding,” where light from the
Cepheids blended with that of adjacent stars.
-
- For many astronomers, the prospect of
looking deeper into the Universe meant that these errors would become visible.
Accounting for this effect is made all the more difficult thanks to intervening
dust in the interstellar and intergalactic medium (ISM, IGM) that naturally
obscures visible light.
-
- Thanks to Webb’s sharp imaging capabilities
at infrared wavelengths, astronomers can now see through the obscuring dust and
get a clearer look at distant Cepheids. Combined with Hubble’s observations,
the “SH0E” team determined that Hubble‘s observations were correct. As a
result, scientists are left with only one explanation for the Hubble Tension,
which is that there is an unseen force responsible for how the cosmos is
expanding:
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- Combining Webb and Hubble gives us the best
of both worlds. We find that the Hubble measurements remain reliable as we
climb farther along the cosmic distance ladder. We need to find out if we are
missing something on how to connect the beginning of the Universe and the
present day.
-
- Next-generation telescopes will investigate
this mysterious unseen force in the coming years by measuring its influence on
cosmic expansion. This includes NASA’s upcoming “Nancy Grace Roman Space
Telescope” and the “ESA’s Euclid mission” (which launched on July 1st, 2023).
Paired with additional data obtained by Webb, these observations will allow
astronomers to test “early Dark Energy” and other theories that attempt to
explain the observations of Hubble and Webb.
-
- In the meantime, the so-called “crisis in
cosmology” will persist, but perhaps not for long.
-
April 28, 2023 UNIVERSE
EXPANDING - how to measure it? 4445
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------ “Jim Detrick” -----------
--------------------- --- Sunday, April 28, 2024
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