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How Can We Be So Sure That Mysterious Dark Matter Exists?

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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

This article is republished from The Conversation under a Creative Commons license. Read the original article

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Vatican Knows More About UFOs Than Intelligence Agencies

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Are you still sure that intelligence agencies and scientists know more about extraterrestrial civilizations than anyone else? In fact, science centers, the CIA, and individuals like Elon Musk and Bill Gates know less about UFOs and alien visitations than the Pope. You may be surprised to learn that the Vatican has its own space exploration program.

The Vatican Observatory is an astronomical research and educational institution supported by the Holy See. Originally based in the Roman College of Rome, the Observatory is now headquartered in Castel Gandolfo, Italy, and operates a telescope at the Mount Graham International Observatory in the United States.

Indirect confirmation that the Vatican is “in the know” are the statements of Pope Francis and his predecessor about extraterrestrial life.

Cultists have repeatedly pointed out that people will soon get acquainted with extraterrestrial intelligence, learn more about extraterrestrial civilizations. And there is no doubt that the Vatican takes extraterrestrials more than seriously. For example, the possibility of converting them to Catholicism has been announced.

“Honestly, I wouldn’t know how to answer that,” the Pope replied, explaining that while scientific knowledge has so far ruled out the possibility of other thinking beings in the universe, “until America was discovered, we thought it didn’t exist, and instead it did,” Pope Francis said.

“But in any case, I think we should stick to what scientists tell us, still aware that the Creator is infinitely greater than our knowledge.”

Francis said the one thing he is sure of in the universe and the world we live in is that it is “not the result of chance or chaos,” but rather of divine intelligence.

Yes, the Vatican’s research power pales in comparison to NASA’s latest technological advances, but the facts speak for themselves.

Until the 19th century, this religious organization was known for opening astronomical observatories and scientific schools where young and able scientists were trained in the technique of observing space.

The Vatican Observatory, which still exists today, is one of the oldest and most authoritative on a planetary scale.

But that’s not all. It turns out that the Vatican also has a space program that, according to experts, is not much inferior to the program of the same NASA.

The Vatican has quite modern and powerful telescopes and other observation equipment. The largest telescope observes the universe in the infrared range and significantly exceeds the capabilities of analogues.

And another interesting fact to ponder. While the Vatican conducts space research, more and more people on Earth begin to believe in the reality of extraterrestrial life.

According to statistics, in 1990 this number was estimated at 27% of the world’s population. In 2000 it increased to 33%. Now it is approaching the 65% mark. Thus, the Vatican’s awareness of extraterrestrial life can be seen as a “fire of knowledge”.

Jesuit Father Jose Funes, director of the Vatican Observatory, said Christians should consider alien life as an “extraterrestrial brother” and part of God’s creation.

Father Funes said it is difficult to rule out the possibility that other intelligent life exists in the universe, and he noted that a field of astronomy is now actively searching for “biomarkers” in the spectral analysis of other stars and planets.

These potential forms of life could include those that do not require oxygen or hydrogen, he said. Just as God created multiple forms of life on Earth, he said, there may be multiple forms of life throughout the universe.

“This is not contrary to faith, because we cannot place limits on God’s creative freedom,” he said.

“To use the words of St. Francis, if we consider earthly creatures to be ‘brothers’ and ‘sisters,’ why can’t we also speak of an ‘extraterrestrial brother,'” he said.

According to some scientists, the goals and objectives of church officials have changed somewhat. Now they are clearly focused on preparing humanity for an encounter with extraterrestrials.

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Potential ‘portal’ discovered that could be a wormhole in our galaxy

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Science has long been interested in the so-called wormholes. These are tunnels in space-time, giving, so far only theoretically, the possibility of instantaneous movement between galaxies.

Recently, for the first time, it turned out that in our Galaxy there is an object similar to a wormhole. It is located at a distance of 1566 light years from us, by space standards within easy reach.

Portals between universes or galaxies are theoretically possible, their existence does not contradict the laws of physics. Albert Einstein and Nathan Rosen stated this back in the 1930s.

Later, several theories appeared, in their own way explaining the likelihood of such travel using the so-called wormholes.

One such hypothesis compares a wormhole and a black hole. The entrances to them as a region of powerful gravity are very similar. Based on this analogy, scientists hope that tunnels in space-time can be detected, including using the Event Horizon Telescope (EHT), the main purpose of which is to observe black holes.

EHT is a complex of radio telescopes located in different parts of the world. With his help, several discoveries have already been made, last year he found a black hole in the center of our native galaxy

In general, there are supposedly millions of such black holes in the Milky Way, and most importantly, some of them are potentially the mouths of wormholes.

Astrophysicists in the United States and Germany recently discovered the first such object. This is Gaia BH1, an object ten times the size of the Sun, located 1566 light-years from Earth.

Gaia BH1 has a Sun-like star orbiting it. Usually, in such binary systems, the black hole is “fed” by the star, simultaneously emitting powerful X-rays. But this black hole does not attract matter to itself and does not radiate anything. Astronomers conventionally call such mysterious objects “sleeping” black holes. They have never before been found in our galaxy.

This is either a “sleeping” black hole, or a perfectly suitable candidate for the “role” of a wormhole. The discovery was made possible by the highly functional Gaia space telescope and the ground-based Gemini telescopes.

Traditionally, a classical wormhole is represented as a three-dimensional tube in a curved two-dimensional space. This does not contradict general relativity, but most scientists believe that such tunnels are only stable if they are filled with exotic matter of negative energy density, which creates a strong gravitational repulsion and prevents the cavity from collapsing.

However, there are also other opinions. For example, Pascal Koiran, professor of computer science at Ecole Normale Superieure of Lyon, published calculations according to which exotic matter is not needed to pass through the wormhole at the level of elementary particles.

Traveling through a wormhole could look like a surreal and disorienting experience. It may appear as if you are traveling through a tunnel of bright light and time is passing by quickly.

You may feel as if you are being transported from one place to another without actually moving. As you move through the wormhole, you could experience changes in gravity or shifts in the space-time continuum.

The inside of the tunnel may appear to be made out of strange and exotic particles, with colors and shapes that seem out of this world. In some cases, the tunnel may even be filled with a mysterious form of energy that seems to be alive.

Wormholes were and remain today the only chance for interstellar flights. So scientists will continue their research, no matter how fantastic they may seem.

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