British Columbia

UBC researchers propose answer to fundamental space problem

UBC scientists say they've found a solution to reconcile two important theories in astrophysics that individually work but have so far been mutually incompatible.

The theories of general relativity and quantum mechanics can coexist according to new research

Everything in our universe can be explained by the theory of relativity and quantum mechanics — except how the two can exist simultaneously. (M. Kornmesser/ESO)

Physicists have been trying to unite the discipline's dominant theories of quantum mechanics and general relativity into a grand unifying theory for years — and a group of University of British Columbia researchers think they might finally have made some progress towards a solution.

The theories of quantum mechanics and general relativity are the two best ways we have to describe how the universe works.

Quantum mechanics is a branch of physics that examines the natural world at the sub-atomic level. 

Einstein's theory of general relativity explains phenomena on a grander scale like black holes or how light travels through a galaxy.

While each theory works well to describe phenomena in its respective area, they are mutually incompatible, according to Jaymie Matthews, a professor of astronomy and astrophysics at the University of British Columbia.. 

Even famed Cambridge University mathematics professor Stephen W. Hawking switches between the theories of quantum mechanics and general relativity, Matthews says. (Kimberly White/Reuters)

"General relativity has passed every test that has been put to it. Quantum mechanics  as a theory has passed every test that has been applied to it," explained Matthews.

"But if you try to take general relativity to the tiniest scales, it kind of breaks down, and if you take quantum mechanics to the largest scale, it breaks down."

The solution has been to use the theories in their respective areas and kind of avoid the "elephant in the universe" incompatibility issue.

"That profound disagreement between general relativity and quantum mechanics disturbs people."

New paper presents a solution

A new paper by three UBC scientists attempts to reconcile these two theories by addressing the problem of our expanding universe.

Astronomers say the universe is constantly expanding at an ever-increasing rate which suggests something, which scientists refer to as dark energy, is pushing it out.

When physicists apply quantum mechanics to this problem, they theorize the energy in question must be incredibly dense.

But the theory of relativity says energy with this much density would have a strong gravitational effect which some scientists maintain would cause the universe to explode, which, of course, hasn't happened.

In their paper, UBC PhD students Qingdi Wang and Zhen Zhu, along with physics and astronomy professor Bill Unruh, have devised a formula where they say the value of this force is fluctuating wildly between positive and negative values and the net result is almost zero. 

This accounts for both the zero density and the ever-increasing expansion.

The paper says we can't feel the movement because it is very, very small.

"This happens at very tiny scales, billions and billions times smaller even than an electron," described Wang in a news release.

A theory of everything

The research is important because if it is well-received, it could put us closer to a uniform theory of everything.

"If quantum mechanics and general relativity can agree with one another, there is no disturbing cosmological elephant in the universe. That would remove one of the most frustrating things,"  Matthews said.

Listen to the interview with Jaymie Matthews on CBC's The Early Edition:

"We like to think we live in an elegant universe," he added. "This would be one step closer to a grand unified theory in which you could describe the universe on a piece of paper."

The research paper was published in Physical Review D last week.