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Dark matter: Should we be so sure it exists? This is how philosophy can help

More than 50 years have passed since astronomers first proposed "dark matter," which is considered the most common form of matter in the universe. Even so, we have no idea what dark matter is. No one has seen dark matter directly or produced it in a lab. But are there competing theories that explain the same data better?

The galaxy cluster Abell 520, with parts suspected of being dark matter highlighted in blue. NASA
The galaxy cluster Abell 520, with parts suspected of being dark matter highlighted in blue. NASA

By Antonis Antonio, PhD student in Philosophy of Science, University of Bristol

More than 50 years have passed since astronomers first proposed "dark matter," which is considered the most common form of matter in the universe. However, We have no idea what is dark matter No one has seen dark matter directly or produced it in a lab. But are there competing theories that explain the same data better?

So how can scientists be so sure it exists? It turns out that philosophy can help us answer these questions.

Back in the 70s, seminal research by astronomers Vera Rubin and Kent Ford about how our neighboring galaxy Andromeda rotates revealed A surprising inconsistency between theory and observation. According to our best gravitational theory - Newton's laws – Stars and gas in a galaxy should rotate more and more slowly the farther they are from the center of the galaxy. This is because most of the stars will be close to the center, which will create a strong gravitational force there.

Rubin and Ford's findings showed that this was not the case. Stars on the outer edge of the galaxy moved about as fast as the stars around its center. The idea that the galaxy must be embedded in a large halo of dark matter was originally proposed to explain this anomaly (although others have suggested this before). This invisible mass interacts with the outer stars through gravity to increase their speeds.

This is just one example of several anomalies in cosmological observations. However, most of them can equally well be explained by modifying the current gravitational laws of Newtonian dynamics and general relativity of Einstein. Maybe nature behaves a little differently on certain scales than these theories predict?

One of the first theories of this kind, developed by the Israeli physicist Mordechai Milgrom in 1983, suggested that Newton's laws may work slightly differently when very small accelerations are involved, such as at the edge of galaxies. This change perfectly matched the observed galactic rotation. Nevertheless, physicists today overwhelmingly favor the dark matter hypothesis incorporated in the so-called model ΛCDM (Lambda's cold dark matter).

This view is so firmly rooted in physics that it is called 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 wonders if we have good reasons to favor one over the other.

The graph shows the rotation speed of stars and gas (vertical axis) as a function of their distance from the center (horizontal axis). Theory suggests we should get the graph labeled 'expected by the visible disc', but reality is different. Wikipedia, CC BY-SA

Why does the scientific community have a strong preference for the dark matter explanation over changes in gravity? And how can we ever decide which of the two explanations is correct?

Philosophy comes to the rescue

This is an example of what philosophers call "Sub-definition of the scientific theory” by the available evidence. It describes any situation where the available evidence may be insufficient to determine what beliefs we should hold in response. This 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 unobserved matter or to the fact that our current laws of gravity are incorrect.

That's why scientists are looking for additional data in other contexts that will eventually clarify the answer to the question. One of the examples of this is in favor of dark matter comes from the observations About how matter is distributed in the Bullet galaxy cluster, which consists of two colliding galaxies about 3.8 billion light-years from Earth. The second is based on measurements of the way light is deflected by (invisible) matter in the cosmic microwave background radiation - the light left over from the big bang. These are often seen as indisputable evidence in favor of dark matter, because Milgrom's original theory cannot explain them.

However, following the publication of these results, additional theories of different gravity were developed during the last decades in order to explain all the observational evidence for dark matter, sometimes successfully Great. However, the dark matter hypothesis still remains the preferred explanation for physicists. Why?

One way to understand this is to use the philosophical tools of Bayesian confirmation theory. It is a probabilistic framework for assessing the extent to which hypotheses are supported by the available evidence in different 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 the evidence) and the ratio between the probabilities that the evidence appears in each case (called the likelihood ratio).

A comparison of the dark matter theory versus the variable gravity theories, where Pr means probability. Courtesy of the author
A comparison of the dark matter theory versus the variable gravity theories, where Pr means probability. Courtesy of the author

If we accept the fact 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. This means that 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 here it turns out that philosophical analysis is helpful.

In the heart Philosophical literature In this issue lies the question of whether the initial probabilities of scientific hypotheses should be determined objectively based on probabilistic laws and rational constraints only. Alternatively, they can include a number of other factors, such as psychological considerations (whether scientists favor a particular hypothesis based on interest or for sociological or political reasons), background knowledge, the success of a scientific theory in other fields, and so on.

Identifying these factors will ultimately help us understand the reasons why the dark matter theory is overwhelmingly favored by the physics community.

Philosophy cannot ultimately tell us whether astronomers are right or wrong about the existence of dark matter. But he can tell us whether astronomers do have good reasons to believe in it, what those reasons are, and what it will take for modified gravity to become as popular as dark matter.

We don't know the exact answers to these questions yet, but we're working on it. More research in the philosophy of science will help us reach a conclusion.

For an article in The Conversation

12 תגובות

  1. In response number 10 from a few days ago, I showed a method for explaining the reason for the rotation of the spiral galaxies, I expected the science responders to help me, but, the science responders were apparently tired and did not cooperate. But, nevertheless, I will give the solution:-
    The solution I came to is not gravitation (!) but the pressure difference that exists throughout the universe, therefore, there is no need for dark matter and this also explains the accelerated expansion of the universe without dark energy!. Everything is explained in articles 75-85, a simple universe.
    And good luck to Yair Lapid who started his job today:-
    Our new Prime Minister for the next four months.
    Please respond gently
    Sabdarmish Yehuda

  2. I have a suggestion for the science responders!
    Let's do a "wisdom of the crowd" exercise together, and try to find the correct logical solution to the aforementioned cosmological problem, which is explained with the help of gravitation and dark matter... I'll start, and you will complete.

    The idea is simple:-
    In the first step - define the problem,
    In the second step - we will find all the more or less successful options for a solution, - I found about 20 solutions,
    In the third stage - we will sift through all the unsuccessful options, - I sifted through about 20 solutions.
    In the fourth step - we will decide which solution is preferable from the rest. - I was left with 2 solutions.

    It is clear to you that if we do the above four steps perfectly we must reach a successful solution!
    Here I need the responders of science, - as the wisdom of the masses.

    Let's start-
    Below is the first step: - defining the problem:

    The gravitation formula of star m in the spiral galaxy M is given: F=M*m*G/r^2

    This gravitation causes the rotational movement of star m in the galaxy: F=(mv^2)/r

    These two formulas should be equal, but they are not. What could be the reasons for this?

    We will move to the second stage and collect all the possible solutions for the solution, at this stage, without paying attention to their correctness. Here are the options:-

    A. At least one of the members of the two formulas M m G rv must be different in size, for example M .
    B. Correcting at least one of the formulas, for example correcting the rotational formula (MOND theory)
    third. Replacing the formulas with other formulas, for example - electricity, magnetism, mechanical force, the strong force, the weak force, the Casimir effect
    d. An external influence, such as the centrifugal force of the entire universe, another dimension, a parallel/twin universe, a living being, a higher power.

    So far all the possibilities I have found, and before we move to phase C, the sifting phase, I expect the scientific readers to make their comments, and perhaps, to upgrade and find more options for a solution?.
    Please respond gently
    Sabdarmish Yehuda

  3. I have a much better solution to the dark matter puzzle. Our universe is just one of many. Our universe is arranged in space according to the shape of a diamond, which we would expect to find, so that each of its twenty faces
    Bordering another universe. The dark force is the gravitational force of the universes surrounding us. A ratio of one to twenty is key. Our universe is one, all observable matter, all atoms and particles make up five percent. The twenty are the universes around our universe, of course they are much, much more, but in the structural arrangement in the space of the honeycomb structure that Eshrimon allows for "holding" and prevents collapse.

  4. When you are a "scientist" advocating a theory that you do not know how to explain - it is a sign that you are very close to the death of the theory.
    "Scientists" - keep talking and leave the world alone.

  5. Unveiled seminal research by astronomers Vera Rubin and Kent Ford about how our neighboring galaxy Andromeda rotates revealed a surprising inconsistency between theory and observation.

    A completely crooked sentence in terms of structure, phrasing and logic

  6. Nothing was said. The writer articulates our basic probability intuition in high terms, concludes that it is actually impossible to know what the probability is for each of the hypotheses, points out that if there are political or sociological biases this can have an effect (but does not say anything about what kind of biases can be expressed in relation to the aforementioned investments), And he concludes that the philosophy of science can perhaps help, but does not explain how.

  7. The article states that more than 50 years have passed since astronomers proposed the concept of dark matter. This is technically true, but it is more accurate to write that it has been 100 years since astronomers first proposed the concept of dark matter:….55..302K/abstract

  8. When I read "According to our best gravitational theory - Newton's laws -" - I stopped reading the article

  9. Investigating reality by way of physical geometric imagination.

    The simple and visible geometry teaches us how to approach the mysterious physics that is not visible to man.
    First, the fundamental concept of geometry must be recognized, and this is an easy recognition.
    The line is the fundamental concept of geometry, and has a millimeter length and shape.
    (there is a straight line, there are infinite shapes of a closed circular line, and there are infinite shapes of a curved line),

    Now we must look for the fundamental concept of physics, similar to the fundamental concept of geometry, and we will inevitably arrive at energy as some size, with many forms.
    The size that must be is not yet clear, but the shapes are completely clear.
    There is energy of heat, and of cold, and muscle energy, and energy of springs, and energy of height, and electrical energy, and chemical energy, and on and on

    Physical geometric similitude guides the neural view in the study of reality.
    A selected line has a quantitative size in millimeters, and is one of many shapes.
    Energy has a quantitative size (not yet clear) and many forms.

    This method of physical geometric similitude immediately yields a law that exists in reality.
    The forms of energy alternate with each other, and the amount exchanged is always preserved.
    Now it is already clear that there is a similarity between geometry and physics, but physics is much more complex, because it has a natural law "the law of conservation of the quantity of energy forms"

    Indeed, physics is much more complex than geometry, because apart from energy, there is another quantitative thing in it and that is the passive time.
    Passive time is a measured quantitative thing, and has the characteristics of absolute rest and absolute cold.
    Passive time fills the infinite space, it does not interfere with the movements of the stars, and is the necessary medium for the transmission of sunlight, in the style of "passive time waves".

    Passive time does not exist in the Newtonian universe, nor does it exist in Einstein's universe.
    With these two great researchers, only active time exists, which exists only in human consciousness. The clear concept of active time is "listening" to the heartbeat.
    Between every two heartbeats we occupy an amount of active time, which fades and disappears immediately.

    Compared to the active time that disappears from reality as soon as it is noticed, the passive time exists and is always there, and is the medium in which light waves move.

    The passive tense has a very important role in the neural view, because matter is seen as a physical form, resulting from the addition of quantities of "two other quantitative things" and they are
    Passive energy and time.
    This is how the shape of the square is perceived by adding quantities of "two other quantitative things" and they are
    The length of a closed line made up of 4 straight line segments of equal length, and within it an amount of space.

    This is not the end of the wonders of neurophysics.
    Just as there is passive time, there is also passive energy that does not change.
    Every real body is made up of sums of passive time and energy, and when such a body is placed on an open spring resting on the surface of the earth, the spring will contract a little.
    A compressed spring exhibits an amount of energy, and it comes from the body resting on the spring.
    The law of conservation of energy also applies to passive energy.

    Neurophysics presents a new reality, without quantum matter with gravity, and of course without dark matter, without electromagnetic waves but with waves of passive time,
    There is no gravity, and no particles, but there are 5 continuous quantitative things in the world.
    Length, area, volume, time and energy.

    And the rest will be told in the article "A wonderful universe built from energy and passive time"

    A. Asbar

  10. In terms of the initial probabilities at the rational level, the question may actually be what is more likely:
    1. A hypothesis regarding a new concept of "matter", which we have no substantial idea about so far except for the "requirement" (- which is a kind of assumption that presupposes the requested -) that it activates and will only act gravitationally (this is the case with the dark matter hypothesis); or,
    2. A correction is required in the rules of the theory, such as a certain change in Newton's laws when a very small acceleration is involved (in Milgrom's theory).
    It seems that the first alternative means an extreme paradigmatic-conceptual change. This is a hypothesis, not yet a scientific theory, and its preference requires the presentation of unequivocal, theoretical and empirical evidence, and at the same time - which will cast doubt on any alternative explanation. Sufficient evidence is in this case a problematic matter, since without the construction of a conceptual infrastructure the theoretical infrastructure is in doubt, and the prediction at the quantitative level may also be a biased "ordering" of results in advance, or a kind of guesswork.
    It seems that the second alternative means only a local theoretical change. It is enough for her to explain the relevant phenomena to a theoretically satisfactory degree and to predict the results quantitatively at an acceptable level.

    The ratio of the final probabilities between the alternatives is not clear, for now. The relative prominence of dark matter theory appears to be a function of general fashionable psychological, social, and cultural factors. It turns out that the scientific world is influenced by the general social and cultural world, where people still believe in "progress" and on the other hand pursue fashionable thrills. In these respects, the conceptual revolution of dark matter is arguably more creative than the relative conservatism of any competing theory.
    In the end, the formulations in question in the initial probabilities are perhaps complex forms of formulation of the "Ockham's razor" principle. However, this principle, as well as the rules of initial and final probabilities, are not law, but preferences of an honest philosophical mind, and therefore the recognition of the question of the first probability will be directly affected by the research effort.

    In the empirical research aspect, attention should be focused not only on attempts to "prove" the existence of dark matter, whatever it may be (such attempts have so far failed completely), but also on accurate measurement of accelerations at the edges of certain galaxies, where anomalies are detected, and on an attempt to discover influencing factors relevant (gas clouds, objects with unusual high-density gravity, such as black holes or neutron stars, etc.) - but also in those galaxies where the measured accelerations are not abnormal compared to the accepted theory. The accuracy and refinement of the empirical findings may very well advance the field.
    In the theoretical field, studies that offer modifications to the accepted theories should certainly be encouraged.
    In any case, what is wrong to do is to assume the correctness of the dark matter hypothesis as if it were a real scientific "theory", when it suffers from an obvious theoretical deficiency.

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