The quest to understand dark matter and dark energy is one of modern science’s most perplexing questions.
Now, one physicist has proposed a controversial solution: dark matter is nothing more than an illusion.
According to Professor Rajendra Gupta of the University of Ottawa, astronomers haven’t been able to find any dark matter particles because they simply do not exist.
Instead, Professor Gupta argues that the effects attributed to these ‘exotic matters’ can be explained by the fundamental forces of the universe changing over time.
The laws of physics, which scientists use to make predictions about the world, are underpinned by constants, such as the speed of light and the force of gravity.
However, according to some physicists, these ‘constants’ aren’t actually all that constant.
Instead, these fundamental features evolve and change as the universe ages in a way that might explain why it looks like we have dark matter and dark energy.
In his paper, Dr Gupta claims: ‘Dark matter and dark energy…may be considered emerging from the weakening of the forces of nature in an expanding Universe.’
The quest to understand dark matter is one of modern science’s most pressing questions. But now, one physicist says that dark matter could be nothing more than an illusion (artist’s impression)
Scientists first started taking dark matter seriously in the 1970s when the astronomer Vera Rubin noticed that galaxies’ outermost stars were rotating much faster than expected.
These strange gravitational effects suggested that galaxies contained more mass than their visible matter could account for, which scientists called dark matter.
Dark energy, meanwhile, was proposed as an extra hidden force to explain why the universe’s expansion has accelerated since the Big Bang.
Scientists currently estimate that dark matter makes up around 27 per cent of the universe, while dark energy makes up about 68 per cent – leaving normal matter to account for a meagre five per cent.
This theory, known as the Lambda Cold Dark Matter Model (ΛCDM), works really well to explain everything from supernovae to the Big Bang.
The problem is that, even after 50 years of research, scientists still have no idea what dark matter or dark energy really are.
Professor Gupta’s idea is to try to explain everything that dark matter currently does, without the need for any strange forces or exotic particles.
The basic idea is that, if the fundamental constants vary, we can take those varying ‘covarying coupling constants’ and put them into Einstein’s equations for cosmic expansion.
Scientists think that dark matter makes up about 80 per cent of all matter in the universe, but it isn’t directly visible. Instead, scientists infer its existence from its gravitational interactions with other objects
When we do this, we get two purely mathematical terms called alpha–matter and alpha–energy that behave just like dark matter and dark energy.
What makes this theory really interesting is that the amount by which the constants vary changes depending on how much matter is concentrated in one place.
At the heart of a galaxy where there is lots of normal matter, physics behaves just like we would expect.
However, out in the far–flung edges of a galaxy where matter is very sparse, the constants become weaker and the effects of alpha–matter become more noticeable.
This means there is a point at which matter became sparse enough for alpha–matter and alpha–energy effects to take over from conventional physics, known as the ‘turn–off density’.
According to Professor Gupta, this explains why galaxies’ outermost stars are moving faster than they should be compared to stars in the inner core.
In his new paper, Professor Gupta compares his model’s predictions to real observations of seven galaxies of varying sizes.
The model reproduced the curve of the rotating galaxy and predicted where the turn–off density would need to be.
Instead of proposing that the universe is filled with dark matter like other scientists have done, Professor Rajendra Gupta, of the University of Ottawa, thinks that the supposed effects of dark matter can be explained by changes in the universe’s fundamental constants. Pictured: The largest map of dark matter ever produced
Across the seven galaxies, the required turn–off density varied by a factor of four, despite the size of the galaxies varying by a factor of eight.
Professor Gupta argues that this consistency suggests that alpha–energy and alpha–matter are real features of the universe and not just theoretical contrivances.
If that is right, then scientists could get rid of dark matter and dark energy from their theories and still explain everything about the universe.
Professor Gupta says: ‘The emergent alpha–matter and alpha–energy can, in principle, replace dark matter in galaxy clusters and assist in galaxy formation.
This theory also makes predictions, which scientists should be able to test.
If alpha–matter has less of an effect when the universe is denser, then more distant galaxies seen further back in time should be more dominated by the effects of visible matter.
However, the big problem for Professor Gupta’s theory is that there is no more evidence that universal constants are variable than there is for the existence of dark matter particles.
There is currently no evidence to suggest that something like the speed of light or the gravitational constant has ever been different, and assuming that they are would require major changes to our theories about the universe.
If this is right, then projects that are attempting to map dark matter, such as the Dark Energy Survey Collaboration (pictured), are simply wasting their time
Observations of extremely distant and bright objects known as quasars show that, even much closer to the Big Bang, these constants are just the same as they are now.
If Professor Gupta is right, and dark matter really is an illusion, it would mean that astronomers have wasted huge amounts of funding on sophisticated telescopes to search for something that doesn’t exist.
Professor Gupta is planning to extend his approach to analyse gravitational lensing and galaxy cluster dynamics, which would be a good test for the theory.
But, with dark matter currently being our best bet about the nature of the universe, a lot more evidence will be needed to overturn the scientific consensus.
Dark matter: The mysterious substance that makes up 85% of the universe that scientists cannot confirm
Dark matter is a hypothetical substance said to make up roughly 85 per cent of the universe.
The enigmatic material is invisible because it does not reflect light, and has never been directly observed by scientists.
Astronomers know it to be out there because of its gravitational effects on known matter.
The European Space Agency says: ‘Shine a torch in a completely dark room, and you will see only what the torch illuminates.
Dark matter is a hypothetical substance said to make up roughly 27 per cent of the universe. It is thought to be the gravitational ‘glue’ that holds the galaxies together (artist’s impression)
‘That does not mean that the room around you does not exist.
‘Similarly we know dark matter exists but have never observed it directly.’
The material is thought to be the gravitational ‘glue’ that holds the galaxies together.
Calculations show that many galaxies would be torn apart instead of rotating if they weren’t held together by a large amount of dark matter.
Just five per cent the observable universe consists of known matter such as atoms and subatomic particles.
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