More than 50 years ago, astronomers initially hypothesized “dark matter,” which is supposed to be the most common form of matter in the cosmos. Despite this, we have no idea what it is because no one has seen it or produced it in the lab.
So, how do scientists know it exists? Is that what they should be? Philosophy, it turns out, can assist us in answering these problems.
But before we dive into Philosophy, lets do a quick read about what is this Dark Matter.
The vast majority of matter in the cosmos is made up of dark matter, a mystery non-luminous element. Its been there since the beginning of time. Its the mysterious “glue” that holds our galaxies , stars and everything in the space together.
In an attempt to detect Weakly Interacting Massive Particles (otherwise known as Dark Matter), physicists have built massive detectors and buried them deep underground to protect them from cosmic rays, but no experiment has found evidence for them.
Why is it that the scientific community prefers the dark matter hypothesis to modified gravity? And how are we ever going to know which of the two explanations is correct?
This is an example of “underdetermination of scientific theory” by existing evidence, as defined by philosophers. This refers to any scenario in which the data supplied is insufficient to identify which ideas we should hold in response.
So with that theory applied, the data alone cannot tell whether the observed velocities are attributable to the presence of additional unobservable matter or to the fact that our existing gravitational equations are inaccurate.
Two Hypothesis were proposed (among many) to look for additional data in other contexts that will eventually settle the question.
- The observations of how matter is dispersed in the Bullet cluster of galaxies, which is made up of two colliding galaxies roughly 3.8 billion light years from Earth.
- Another is based on observations of how light is deflected by (invisible) matter in the cosmic microwave background, which is the light left over from the big bang.
However, in the decades since these findings were published, more modified gravity theories have been developed to account for all of the observational evidence for dark matter, with varying degrees of success. Yet, the dark matter hypothesis still remains the favourite explanation of physicists. Why?
The philosophical tools of Bayesian confirmation theory can be used to help understand. This is a probabilistic framework for estimating the degree to which hypotheses in diverse situations are supported by the available evidence.
The above formula explains that, the product of the initial probabilities of the two hypotheses (before evidence) and the probabilities that the evidence appears in each case determines the ultimate probability of each hypothesis in the situation of two competing hypotheses (called the likelihood ratio).
The likelihood ratio is equal to one if we agree that the most complex versions of modified gravity and dark matter theory are equally supported by evidence. That is, the final conclusion is based on the probabilities of these two hypotheses in the outset.
One of the most challenging difficulties in Bayesian confirmation theory is determining what exactly counts as a hypothesis’s “initial probability” and the various methods for determining such probabilities. And it is here that philosophical analysis comes in handy.
The question of whether the beginning probability of scientific hypotheses should be objectively calculated based purely on probabilistic laws and rational restrictions is at the heart of the philosophical literature on this topic. Alternatively, they could include psychological considerations, background knowledge, the success of a scientific theory in other disciplines, and so on.
Identifying these characteristics can help us better understand why dark matter hypothesis is so widely accepted in the physics community.
In the end, philosophy cannot tell us whether astronomers are correct or incorrect concerning the existence of dark matter. However, it can tell us whether astronomers have solid reasons to believe in modified gravity, what those reasons are, and what it would take for modified gravity to catch up to dark matter in popularity.
Can philosophy really help scientists in answers the most unanswered question in all time? Only time will tell.
What are your thoughts on this? Comment below.