The current, best model of particle physics only explains about 5% of the known universe, according to a physics journal.

The model, known as the Standard Model, was described by the journal as “the most rigorous theory of particle physics, incredibly precise and accurate in its predictions” – and yet it doesn’t explain 95% of what we know as reality.

“For the past 50 years such a system has allowed scientists to incorporate particle physics into a single equation that explains most of what we can see in the world around us,” wrote Symmetry Magazine. “Despite its great predictive power, however, the Standard Model fails to answer five crucial questions, which is why particle physicists know their work is far from done.”

The five questions listed are:

1) Why do neutrinos have mass?
2) What is dark matter?
3) Why is there so much matter in the universe?
4) Why is the expansion of the universe accelerating?
5) Is there a particle associated with the force of gravity?

Of those five, the second question is the most well-known to the general public given the near-constant deluge of astronomy articles asking that very question.

But, overall, the revelation of what scientists don’t know hints at the depths of the universe, particularly the mysteries of that veiled reality we can barely see.
It also poses an interesting question: is there a limit of what humans are capable of knowing about the universe, just as a golden retriever has no conceptual ability to understand he’s actually on a ball spinning around in outer space?

For one thing, the study of dark matter is particularly eye-opening: right now researchers think it somehow interacts with normal matter, but so far they haven’t been able to perceive how.

“Scientists realized they were missing something when they noticed that galaxies were spinning much faster than they should be, based on the gravitational pull of their visible matter,” the magazine stated. “They were spinning so fast that they should have torn themselves apart. Something we can’t see, which scientists have dubbed ‘dark matter,’ must be giving additional mass—and hence gravitional pull—to these galaxies.”

“Dark matter is thought to make up 27 percent of the contents of the universe. But it is not included in the Standard Model.”

These unanswered questions reveal the philosophical implications of physics: how exactly is reality defined, and what are the limits of knowable science?