- 4536 - UNIVERSE EXPANDING - measuring different rates? - Astronomers have used the James Webb and Hubble space telescopes to confirm one of the most troubling conundrums in all of physics, that the universe appears to be expanding at bafflingly different speeds depending on where we look.
----------------------- 4536
- UNIVERSE EXPANDING
- measuring different rates?
-
- This problem, known as the “Hubble
Tension”, has the potential to alter or even upend cosmology altogether. In
2019, measurements by the Hubble Space Telescope confirmed the puzzle was real;
in 2023, even more precise measurements from the James Webb Space Telescope
(JWST) cemented the discrepancy.
-
- Now, a triple-check by both telescopes
working together appears to have put the possibility of any measurement error
to bed for good. There may be something seriously wrong with our understanding
of the universe.
-
- With measurement errors negated, what
remains is the real and exciting possibility we have misunderstood the
universe. Currently, there are two
"gold-standard" methods for figuring out the Hubble constant, a value
that describes the expansion rate of the universe. The first involves poring
over tiny fluctuations in the cosmic microwave background (CMB) which is an
ancient relic of the universe's first light produced just 380,000 years after
the Big Bang.
-
- Between 2009 and 2013, astronomers mapped
out this microwave fuzz using the European Space Agency's Planck satellite to
infer a Hubble constant of 46,200 mph
per million light-years, or 67 kilometers per second per megaparsec (km/s/Mpc).
-
- The second method uses pulsating stars
called “Cepheid variables”. Cepheid stars are dying, and their outer layers of
helium gas grow and shrink as they absorb and release the star's radiation,
making them periodically flicker like distant signal lamps.
-
- As Cepheids get brighter, they pulsate more
slowly, giving astronomers a means to measure their absolute brightness. By
comparing this brightness to their observed brightness, astronomers can chain
Cepheids into a "cosmic distance ladder" to peer ever deeper into the
universe's past. With this ladder in place, astronomers can find a precise
number for its expansion from how the Cepheids' light has been stretched out,
or red-shifted. As space expands the
lights wavelength expands.
-
- But this is where the mystery begins.
According to Cepheid variable measurements the universe's expansion rate is
around “74 km/s/Mpc”. This is an
impossibly high value when compared to Planck's measurements. Cosmology had
been hurled into uncharted territory.
-
- Some scientists thought that the disparity
could be a result of a measurement error caused by the blending of Cepheids
with other stars in Hubble's aperture. But in 2023, the researchers used the
more accurate JWST to confirm that, for the first few "rungs" of the
cosmic ladder, their Hubble measurements were right. Nevertheless, the
possibility of crowding further back in the universe's past remained.
-
- 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.
The Hubble measurements remain reliable as we climb farther along the
cosmic distance ladder.
-
- The tension at the heart of cosmology is
here to stay
-
August 10, 2024 UNIVERSE
EXPANDING - measuring different rates 4536
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--------------------- --- Friday, August 16, 2024
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