Our universe is composed of approximately 4,86% ordinary matter, 26,0% dark matter, and 69,1% dark energy.

Dark matter

Dark matter is a form of matter that does not interact with light, hence „dark “. Is does not interact with the electromagnetic force or the strong force (hence not interacting with normal matter). 

However, it does have mass and exerts a gravitational pull, which plays a critical role in the structure of the universe. 

Without dark matter, galaxies would not have been able to form, as the gravitational pull provided by ordinary matter alone would not be sufficient for galaxies and stars to form.

Gravitational lensing

The most compelling evidence for dark matter comes from gravitational lensing -a phenomenon where light bends as it passes near a massive object due to the curving effects it has on spacetime. 

Observations have shown that the amount of bending cannot be explained by visible mater alone, indicating the presence of an unseen mass: dark matter.

Particles of dark matter (WIMPs)

If dark matter consists of particles (as many physicists hypothesize), approximately 100 million of them would be floating through our body every second, moving at incredible speeds, without you ever noticing. 

That is why it is called dark: they basically do not interact with anything, neither with normal matter nor with themselves. 

Physicists refer to those particles as Weakly Interacting Massive Particles (WIMPs). They are thought to interact only through gravity and the weak nuclear force, offering hope for detection. 

Rare collisions between WIMPs and atomic nuclei could produce a faint flash of light, which scientists are actively searching for in specialized detectors.

Dark energy

Dark energy is even more mysterious than dark matter and is believed to be the driving force behind the accelerating expansion of the universe.

In the 1990s it was common knowledge that the expansion of the universe is slowing down, and physicists tried to find the deceleration parameter. This parameter is supposed to tell us about the balance between the outward momentum from the Big Bang and the inward pull of the gravity. A high number of the parameter would indicate the universe collapsing in a Big Crunch under its own gravity. 

It turned out that the deceleration parameter was actually negative, so the expansion of the universe is actually accelerating.

The origins of this parameter can be traced back to Einsteins theory of general relativity. Einstein noticed that his equations of space-time and gravity predicted that gravity should have destroyed the universe long ago. 

Even though this was at a time we knew nearly nothing about the universe, he was able to add the cosmological constant, the parameter, to his equations. The cosmological constant represents a property of space itself-an energy inherent in the fabric of space that acts as a repulsive force, counteracting gravity on large scales. 

However, after the discovery of the universe's expansion by Edwin Hubble, Einstein dismissed it as his „greatest blunder “. Ironically, the cosmological constant is now back in play to explain the accelerating universe.

Other theories propose that dark energy might be a dynamic energy field similar to the cosmological constant but with varying properties over time. Because of our limited understanding, physicists use dark energy as a placeholder term for any phenomenon that could explain this accelerated expansion.

In the early universe, dark energy’s influence was negligible because the universe was smaller and dominated by matter and radiation. 

However, as the universe expanded, dark energy became more significant. About five billion years ago, it began to dominate, driving the accelerated expansion that we observe today.