Since the 1990s, Hubble has gazed upon some of the earliest galaxies Universe. This has allowed astronomers to measure cosmic distance and the Hubble Constant - how fast the cosmos is expanding.
Host | Matthew S Williams
On ITSPmagazine 👉 https://itspmagazine.com/itspmagazine-podcast-radio-hosts/matthew-s-williams
______________________
This Episode’s Sponsors
Are you interested in sponsoring an ITSPmagazine Channel?
👉 https://www.itspmagazine.com/sponsor-the-itspmagazine-podcast-network
______________________
Episode Notes
Since the 1990s, Hubble has gazed upon some of the earliest galaxies Universe. This has allowed astronomers to measure cosmic distance and the Hubble Constant - how fast the cosmos is expanding.
The only problem is that measurements of the local Universe vs. the earliest observable galaxies produce different distance results. This has come to be known as the "Hubble Tension," and its far from resolved.
______________________
Resources
Hacking The Cosmological Distance Ladder - Fraser Cain: https://www.youtube.com/watch?v=JGYHwpsMQ1w
______________________
For more podcast Stories from Space with Matthew S Williams, visit: https://itspmagazine.com/stories-from-space-podcast
The Crisis in Cosmology: What is the Hubble Tension? | Stories From Space Podcast With Matthew S Williams
[00:00:00] The authors acknowledge that this podcast was recorded on the
traditional unceded lands of the Lekwungen peoples. In the 1920s, astronomers
made a startling discovery when observing galaxies beyond our own. These
galaxies, once thought to be nebulas within the Milky Way, were receding from
us. This observation led to the realization that the universe is in a state of
expansion.
It also led to the Big Bang Theory, the most widely accepted cosmological
model for how the universe came to be. By the 1990s, the Hubble Space
Telescope gave astronomers the opportunity to make the deepest views of the
universe ever. While it was hoped that Hubble's observations would resolve
some of the greatest questions in cosmology and astronomy, these observations
only deepened the mystery, as they indicated that the rate of expansion,
otherwise known as the Hubble constant, was [00:01:00] accelerating with time.
This led to the popular notion that a mysterious force was behind cosmic
expansion. Which came to be known as dark energy. However, this was not the
only cosmological mystery that Hubble would deepen. In addition, its
observations at galaxies that existed during the early universe did not agree with
local distance measurements.
The same discrepancy was noticed when the European Space Agency's Planck
mission mapped out the cosmic microwave background. In short, distance
measurements and what they said about the rate at which the universe is
expanding differed depending on the method used and where we looked.
Looking locally produced one set of estimates.
Looking back to the farthest reaches of space and time produced another. This
came to be known as the Hubble tension. Hubblecast Or, the crisis in
cosmology. [00:02:00] And according to the latest observations from the James
Webb Space Telescope, this crisis is far from resolved. As we covered in
previous episodes dedicated to Einstein's revolution and the history of
cosmology, by the early 20th century, scientists had made a number of very
profound cosmological discoveries.
The first was the realization that what appeared to be clouds of nebulous gases,
which astronomers assumed were orbiting within the Milky Way, were in fact
distant galaxies. This was due to improved instruments that could finally resolveindividual stars in these galaxies. Not long thereafter, between 1905 and 1916,
Einstein proposed his revolutionary theory of relativity.
This theory was described in several seminal papers released in 1905, which
described how light behaved in a vacuum, and how speed affects [00:03:00] the
observer's perception of time, space, and mass. This came to be known as
Einstein's theory of special relativity. Between 1905 and 1916, Einstein
expanded the theory to account for gravity.
The end result was his General Theory of Relativity. Which describes how mass
and gravity are related, and how these alter the curvature of space time. Once
this theory was experimentally verified, only three years later, with the
Eddington experiment, scientists began exploring potential resolutions to Quine
Stein's field equations.
Like Einstein, many scientists were concerned that, if correct, his theory
predicted that the universe would be in a state of contraction, eventually being
swallowed up in a big crunch. To resolve this, Einstein added a parameter to his
field equations, which he called the cosmological constant, a mysterious yet
unknown force that held back gravity [00:04:00] and kept the universe in a
static stable form.
However, several physicists noted that depending upon the value of this
parameter, the universe could also be in a state of expansion. This explanation
was used to explain observations made by many astronomers who noted that
galaxies beyond the Milky Way Transcripts provided by Transcription
Outsourcing, LLC.
A possible explanation for this was that the space between our galaxy and those
being observed was expanding. As light traveled through this expanding
medium, the wavelength of the light would be lengthened, causing it to appear
more reddish. A similar phenomenon was happening with the galaxies located
closest [00:05:00] to us, such as Andromeda and the Triangulum Galaxy.
As opposed to redshift, these galaxies exhibited signs of blueshift, where the
wavelength of light coming from them was shifted towards the blue end of the
spectrum, because the space between them and our galaxy was being
compressed. By 1927 and 1929, Belgian priest and astronomer Georges
Lemaître and American astronomer Edwin Hubble independently concluded
that the rate at which the universe was expanding could be calculated.This came to be known as Hubble's Law, or the Hubble Lemaître Law in
recognition of both astronomers independently deriving it, while the rate at
which the cosmos was expanding came to be known as the Hubble Constant. Or
Hubble La Matri constant. The Hubble Space Telescope, which launched in
1990 was so named because one of the main things that it would be
investigating was [00:06:00] the Hubble La Matri constant.
In many respects, Hubble was the culmination of nearly 50 years of lobbying
and research by nasa, while Hubble was not technically the first space telescope
ever to be deployed. It was the first dedicated mission that was capable of
conducting deep field astronomy in the optical, near infrared, and ultraviolet
wavelengths.
Operating in orbit also meant that it was not subject to atmospheric interference,
which for ground based telescopes requires adaptive optics and other methods
that correct for the distortion of light. Prior to Hubble, astronomers could only
see objects in our universe up to a distance of about 4 billion light years, which
effectively meant that they were confined to observing the evolution of the
universe during the past 4 billion years.
Hubble extended this range considerably, first to 10 billion light years, and once
it got into its ultra deep field and extreme deep field programs, It [00:07:00] was
able to observe some of the earliest galaxies in the universe, which existed more
than 13 billion years ago. As mentioned, these observations revealed that
cosmic expansion was accelerating with time.
Whereas the rate had been relatively consistent up until about 9 billion years
after the Big Bang, within the past 4 billion years, it was speeding up. This led
astronomers to reconsider Einstein's cosmological constant. A force that held
back gravity, which they now reimagined as dark energy. Similar in theory to
dark matter, a mysterious invisible mass that constituted most of the matter in
our universe, dark energy was envisioned as a mysterious invisible force that
was working against gravity.
Over time, as the large scale structures of the universe expanded farther and
farther apart, The gravitational attraction between these large structures became
less and less. All this led to the [00:08:00] most widely accepted model of
cosmology that astronomers have been using for decades. It is known as the
Lambda Cold Dark Matter Model.
And whereas Lambda represents the cosmological constant, a. k. a. the Hubble
Lemaître constant, consistent with Einstein's earlier field equations, Darkmatter, referred to a specific theory of dark matter, in which dark matter
particles are large, slow moving, and only interact with normal, or visible
matter, through gravity, the weakest of the four fundamental forces of the
universe.
But as also mentioned, Hubble's observations also led to problems with what is
known as the cosmic distance ladder. This refers to the different methods that
astronomers use for measuring cosmic distances. For local distance
measurements, or objects that are within 10, 000 light years of the solar system,
astronomers will rely on parallax measurements.
This time honored method relies on the [00:09:00] principles of trigonometry,
and consists of measuring the angle of a star relative to Earth at different times
of the year, coinciding with the Earth being in different locations around the
Sun, and comparing the angular separation. The next rung in the ladder, so to
speak, consists of using standard candles for distance measurement.
In astronomy, this refers to monitoring stars for changes in their brightness, or
what is known as a light curve. In this case, astronomers use variable stars, or
stars that are known to vary in brightness over time, in particular, Cepheid
variables, which are known to pulsate in a way that is stable and predictable.
For over a century, astronomers have understood that the pulsations and the
variation of brightness in these stars can yield accurate distance measurements.
And whereas ground based telescopes were able to measure distances of up to
13 million light years, the Hubble Space [00:10:00] Telescope has been able to
make distance measurements using Cepheid variables to distances of up to 100
million years.
For the third rung in the cosmic ladder, astronomers rely on the brightest stellar
objects, such as stars. Type 1a supernovas and how their brightness diminishes
over time. This method allows astronomers to measure the distance to objects
up to a billion light years away. The fourth and final rung in the ladder consists
of measuring cosmological redshift.
Since the early 20th century astronomers use redshift to measure how fast
galaxies were receding from our own. In addition, since the 1960s astronomers
have been aware of the cosmic microwave background. or CMB, the remnant
radiation left over after the Big Bang. This is the furthest form of light that any
telescope can see, and is proof that the Big Bang model of cosmology is in fact
correct.Between the 1980s [00:11:00] and 2010, astronomers have obtained
increasingly accurate measurements of the cosmic microwave background,
including its polarization and redshift, thanks to missions like the Soviet Relict
1. NASA's Cosmic Background Explorer, or COBE, the Wilkinson Microwave
Anisotropy Probe, or WMAP, and the European Space Agency's Planck
spacecraft.
By conducting redshift measurements of the CMB, as well as objects that are
farthest from the Milky Way and at the very edge of detection, in other words,
objects that existed during the early universe, Astronomers are capable of
making distance measurements of up to 13 billion light years. This is where
troubles truly began with Hubble's measurements, when observing galaxies that
existed over 13 billion years ago, only a few hundred million years after the Big
Bang.
Hubble noted redshift values that did not correspond to other distance
measurements. The same [00:12:00] is true of redshift measurements of the
CMB. Whereas, local distance measurements, using parallax and standard
candles, yields a value of about 26, 000 km per hour per megaparsec. Redshift
measurements of the CMB and distant galaxies yields an entirely different value
of roughly 24, 000 kilometers an hour per megaparsec.
In other words, the universe appears to be expanding faster in our vicinity.
While it was hoped that the James Webb Space Telescope would resolve this
crisis in cosmology, it too has only added to the problem. Using its more
advanced optics and advanced suite of scientific instruments, the James Webb
has repeated many of Hubble's observations, which recently included a deep
field's look at galaxies that existed during the early universe.
Unfortunately, Webb's own measurements indicated that Hubble was right on
the money, and that its redshift measurements of these [00:13:00] galaxies were
in fact correct. And so, the Hubble tension remains. These findings have
reinvigorated alternative theories of gravity, such as Modified Newtonian
Dynamics, or MOND.
This view, which is supported by a minority of astrophysicists, essentially states
that the gravitational force within galaxies varies inversely with the radius.
According to one theory of modified gravity, our galaxy may be in the center of
an under density, which would explain why our observations don't match up.
While this theory does present a possible resolution to the Hubble Tension, it
raises other theoretical problems and discrepancies in its place. Other proposedresolutions include modified general relativity, primordial magnetic fields, Or
the existence of dark matter and dark energy that behave differently in the early
universe.
These theories [00:14:00] can generally be divided into two categories. Early
time solutions and late time solutions. Early time solutions offer explanations
that occurred shortly after the Big Bang, while late time solutions occurred
more recently in cosmic history. Early time solutions postulate that the energy
density of the early universe was somehow increased before recombination, the
cosmological epoch during which charged electrons and protons became bound
to form neutral hydrogen mere seconds after the Big Bang.
In a recent study, a team of astrophysicists from John Hopkins University and
the Space Telescope Science Institute argued that a form of early dark energy
existed at this time, which decayed faster than other forms of radiation after
recombination occurred. Big time solutions, on the other hand, postulate that the
energy density in the post recombination universe, roughly 300, 000 years after
the Big Bang, is smaller than what is predicted [00:15:00] by the standard
lambda cold dark matter model.
However, none of these theories offer an immediate resolution, and will need to
be tested and verified based on future observations, not only by the James Webb
Space Telescope, but Hubble's successor, the Nancy Grace Roman Space
Telescope. As well as the European Space Agency's Euclid admission. The UL
admission launched on July 1st, 2023, and has already began collecting its first
light.
The Nancy Grace Roman Space Telescope meanwhile is expected to launch in
late 2026 or early 2027. Both of these observatories will use wide field and
wide angle telescopes to observe how the cosmos has expanded over the course
of billions of years in the hopes of confirming and measuring the influence of
dark energy.
What's more, scientists are forced to await future discoveries in order to resolve
the current scientific problems. And when it comes [00:16:00] to the Hubble
tension, it is clear that this particular crisis in cosmology is destined to continue.
Meanwhile, all we can do is wait, and look forward to the next round of
scientific results and research findings, in the hopes that someday, astronomers,
will be able to say with confidence, we now know how the universe began, and
how it's changed over time, and And all the underlying physics that governs it.That day may never come, but such is the nature of cosmology. It is like an
onion constantly shedding its skin, except we find ourselves on the inside of the
onion, clawing our way out. With every new layer that we shed, we find that the
universe that we inhabit is larger than we previously expected. And that the
laws which appear to govern things on the smaller scales don't necessarily
govern things on the larger scale.
But we keep looking with increasingly sophisticated instruments, [00:17:00]
hoping that someday we'll find our way to the last layer and the last great
cosmological mystery. Thank you for listening. I'm Matt Williams, and this has
been Stories from Space.