It’s supposed to be the most common form of matter in the universe, but nobody has ever actually seen it.
It has been more than 50 years since astronomers first proposed “dark matter”, which is thought to be the most common form of matter in the universe. Despite this, we have no idea what it is – nobody has directly seen it or produced it in the lab.
So how can scientists be so sure it exists? Should they be? It turns out philosophy can help us answer these questions.
Back in the 1970s, a seminal study by astronomers Vera Rubin and Kent Ford of how our neighbour galaxy Andromeda rotates revealed a surprising inconsistency between theory and observation.
According to our best gravitational theory for these scales – Newton’s laws – stars and gas in a galaxy should rotate slower and slower the further away they are from the galaxy’s centre. That’s because most of the stars will be near the centre, creating a strong gravitational force there.
Rubin and Ford’s result showed that this wasn’t the case. Stars on the outer edge of the galaxy moved about as fast as the stars around its centre.
The idea that the galaxy must be embedded in a large halo of dark matter was basically proposed to explain this anomaly (though others had suggested it previously). This invisible mass interacts with the outer stars through gravity to boost their velocities.
This is only one example of several anomalies in cosmological observations. However, most of these can be equally explained by tweaking the current gravitational laws of Newtonian dynamics and Einstein’s theory of general relativity. Perhaps nature behaves slightly differently on certain scales than these theories predict?
One of the first such theories, developed by Israeli physicist Mordehai Milgrom in 1983, suggested that Newtonian laws may work slightly differently when there’s extremely small acceleration involved, such as at the edge of galaxies. This tweak was perfectly compatible with the observed galactic rotation.
Nevertheless, physicists today overwhelmingly favour the dark matter hypothesis incorporated in the so-called CDM model (Lambda Cold Dark Matter).
This view is so strongly entrenched in physics that is widely referred to as the “standard model of cosmology”. However, if the two competing theories of dark matter and modified gravity can equally explain galactic rotation and other anomalies, one might wonder whether we have good reasons to prefer one over another.
Why does the scientific community have a strong preference for the dark mater explanation over modified gravity? And how can we ever decide which of the two explanations is the correct one?
Philosophy to the rescue
This is an example of what philosophers call “underdetermination of scientific theory” by the available evidence. This describes any situation in which the available evidence may be insufficient to determine what beliefs we should hold in response to it. It is a problem that has puzzled philosophers of science for a long time.
In the case of the strange rotation in galaxies, the data alone cannot determine whether the observed velocities are due to the presence of additional unobservable matter or due to the fact that our current gravitational laws are incorrect.
Scientists therefore look for additional data in other contexts that will eventually settle the question. One such example in favour of dark matter comes from the observations of how matter is distributed in the Bullet cluster of galaxies, which is made up of two colliding galaxies about 3.8 billion light years from Earth.
Another is based on measurements of how light is deflected by (invisible) matter in the cosmic microwave background, the light left over from the big bang. These are often seen as indisputable evidence in favour of dark matter because due Milgrom’s initial theory can’t explain them.
However, following the publication of these results, further theories of modified gravity have been developed during the last decades in order to account for all the observational evidence for dark matter, sometimes with great success. Yet, the dark matter hypothesis still remains the favourite explanation of physicists. Why?
One way to understand it is to employ the philosophical tools of Bayesian confirmation theory. This is a probabilistic framework for estimating the degree to which hypotheses are supported by the available evidence in various contexts.
In the case of two competing hypotheses, what determines the final probability of each hypothesis is the product of the ratio between the initial probabilities of the two hypotheses (before evidence) and the ratio of the probabilities that the evidence appears in each case (called the likelihood ratio).
If we accept that the most sophisticated versions of modified gravity and dark matter theory are equally supported by the evidence, then the likelihood ratio is equal to one. That means the final decision depends on the initial probabilities of these two hypotheses.
Determining what exactly counts as the “initial probability” of a hypothesis, and the possible ways in which such probabilities can be determined, remains one of the most difficult challenges in Bayesian confirmation theory. And it is here where philosophical analysis turns out to be useful.
At the heart of the philosophical literature on this topic lies the question of whether the initial probabilities of scientific hypotheses should be objectively determined based solely on probabilistic laws and rational constraints.
Alternatively, they could involve a number of additional factors, such as psychological considerations (whether scientists are favouring a particular hypothesis based on interest or for sociological or political reasons), background knowledge, the success of a scientific theory in other domains, and so on.
Identifying these factors will ultimately help us understand the reasons why dark matter theory is overwhelmingly favoured by the physics community.
Philosophy cannot ultimately tell us whether astronomers are right or wrong about the existence of dark matter. But it can tell us whether astronomers do indeed have good reasons to believe in it, what these reasons are, and what it would take for modified gravity to become as popular as dark matter.
We still don’t know the exact answers to these questions, but we are working on it. More research in philosophy of science will give us a better verdict.
Antonis Antoniou, PhD candidate in Philosophy of Science, University of Bristol
“Alien bases” may be hiding off the coast of Alaska, researchers say
An organization of civilian volunteers dedicated to the study of
unidentified flying objects (UFOs) has issued a statement based on
decades of studying eyewitness reports. According to Mutual UFO Network,
“alien bases” may be hiding off the coast of Alaska, reports the-sun.com.
say the deep waters in this region may hold something surprising. After
analyzing reports from the ship’s crew from 1945, they hypothesized
that alien objects could be lurking underwater, off the coast of the
Alleged sightings of alien spacecraft nearly 80 years ago
have become a key point in research. Members of the organization believe
that UFOs move over water and may have “bases.”
allege crew members on a U.S. Army transporter ship sailing past Island
Adak saw a massive UFO sized 150 to 200 feet emerge from the water.
Although these reports are nowhere to be found, UFO enthusiasts believe
the unidentified flying vehicles likely were used to commute to
different supposed alien bases hiding in the deep waters.
the “secret reports” of the sailors aren’t available, investigators
have taken it upon themselves to unravel the mystery surrounding the
unidentified flying objects and they believe the ocean has alien bases
that humans aren’t aware of.
Enthusiasts claim that UFOs may be
using “underwater networks” or wormholes as superhighways to travel
between points in the universe. UFO researcher Johnny Enoch added that
such objects could serve as a vehicle for aliens.
There are also
theories that other places on Earth could serve as bases for alien life.
A mountain in Seoul, South Korea is believed to be hiding a UFO,
according to Dr. Steven Greer.
An episode of the series “The
Alaska Triangle” features satellite imagery that claims to show one of
the “alien bases” in the Pacific Ocean off the coast of California.
another researcher featured in the program showed markings from the sea
bed that she claimed could have been roadways for aliens.
the mysteries of the ocean remain unsolved, researchers continue their
search, trying to unravel the mystery of what may be hiding in the
depths of the waters off the coast of Alaska.
Enormous City-Size Comet Racing Towards Earth Grows ‘Devil Horns’ After Massive Eruption
A volcanic comet the size of a mid-sized US city has
violently exploded for the second time in four months as it continues
racing toward the earth. And following the massive eruption, the cloud
of ice and gas sprouted what looked like a pair of gigantic devil horns.
The city-sized comet, named 12P/Pons-Brooks, is a cryovolcanic — or
cold volcano — comet. It has a solid nucleus, with an estimated diameter
of 18.6 miles, and is filled with a mix of ice, dust and gas known as
cryomagma. The nucleus is surrounded by a fuzzy cloud of gas called a
coma, which leaks out of the comet’s interior.
When solar radiation heats the comet’s insides, the pressure builds up
and the comet violently explodes, ejaculating its ice-cold innards into
space through seeping cracks in the nucleus’s shell.
Live Science report:
On Oct. 5, astronomers detected a large outburst from 12P, after the
comet became dozens of times brighter due to the extra light reflecting
from its expanded coma, according to the British Astronomical Association (BAA), which has been closely monitoring the comet
Over the next few days, the comet’s coma expanded further and developed its “peculiar horns,” Spaceweather.com
reported. Some experts joked that the irregular shape of the coma also
makes the comet look like a science fiction spaceship, such as the
Millennium Falcon from Star Wars.
The unusual shape of the comet’s coma is likely due to an irregularity in the shape of 12P’s nucleus, Richard Miles, a BAA astronomer, told Live Science after the comet’s previous eruption.
The outflowing gas is likely being partially obstructed by a notch
sticking out on the nucleus, Miles said. As the gas continues to expand
away from the comet, the irregularity in the coma’s shape becomes more
defined and noticeable, he added.
12P is currently hurtling toward the inner solar system, where it
will be slingshotted around the sun on its highly elliptical 71-year
orbit around our home star — similar to the green comet Nishimura, which
pulled off a near-identical maneuver on Sept. 17.
12P will reach its closest point to Earth on April 21, 2024, when it
may become visible to the naked eye before being catapulted back toward
the outer solar system. It will not return until 2095.
This is the second time 12P has sprouted its horns this year. On July
20, astronomers witnessed the comet blow its top for the first time in
69 years (mainly due to its outbursts being less frequent and harder to
spot during the rest of its orbit). On that occasion, 12P’s coma grew to
around 143,000 miles (230,000 km), which is around 7,000 times wider
than the comet’s nucleus.
It is unclear how large the coma grew during the most recent
eruption, but there are signs the outburst was “twice as intense” as the
previous one, the BAA noted. By now, the coma has likely shrunk back to
near its normal size.
As 12P continues to race toward the sun, there is a high probability
that we will witness several more major eruptions. It is possible that
those eruptions will be even bigger than the most recent one as the
comet soaks up more solar radiation, according to Spaceweather.com.
But 12P is not the only volcanic comet that astronomers are currently
monitoring: 29P/Schwassmann-Wachmann (29P) — the most volatile volcanic
comet in the solar system — has also had several noticeable eruptions
in the last year.
In December 2022, 29P experienced its largest eruption in around 12 years, which sprayed around 1 million tons of cryomagma into space. And in April this year, for the first time ever, scientists accurately predicted one of 29P’s eruptions before it actually happened, thanks to a slight increase in the comet’s brightness in the lead-up to the icy explosion.
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