How come gravity is so weak? The nature of space-time itself may contain the solution.

 Examining the Higgs boson in more detail may provide the answer to why gravity is so weak.

An illustration of Earth bending a grid of space-time. (Image credit: Getty Images)

Why, in comparison to the other four fundamental forces, is gravity so weak?

It would still be the weakest force by a factor of a billion billion billion, even if it were a billion times stronger. The odd fragility of gravity stands out, almost begging for an explanation.

Strangely, the Higgs boson's mechanics and the fundamental properties of space-time may hold the key to gravity's weakness rather than gravity itself.

Pick up some paper. Congratulations! You have successfully resisted the planet's total gravitational pull.

Gravity is by far the weakest of the four fundamental forces of nature, therefore it didn't require much effort. In one metric, the strong nuclear force—the strongest of all forces—is a thousand billion billion times weaker than gravity.

Here's another perspective on the gravity's genuine degree of weakness. The Planck mass is the upper bound on the smallest black hole that can be constructed. You may figure it out by multiplying the speed of light by the square root of the lowered Planck constant and Newton's G by that result. It weighs anywhere between 10-8 kilos. You could create even smaller, lighter black holes if gravity were strong—if Newton's G were larger.

The W and Z bosons, which are the weak nuclear force's energy carriers, are roughly 10 quadrillion times lighter than the Planck mass. The weak nuclear force is therefore quadrillions of times stronger than gravity, making it the second-strongest force in the universe after gravity.

Most physicists find this "hierarchy problem" strange. There is no need for an explanation; it might simply be the way the universe is, but that isn't particularly gratifying. Instead, it appears to be a chance to explore the mechanics of the fundamental forces more thoroughly and see if there is anything new we can discover.

Just contrast gravity with its "nearest" opponent, the weak nuclear force, and disregard electromagnetism and the strong nuclear force. We may be able to comprehend the big picture if we can determine why the weak nuclear force is so noticeably greater than gravity.

We don't understand why gravity is as powerful as it is. Nothing that exists in any physics theory seems to explain its power. The Higgs boson, however, is something that seems to explain the characteristics of the weak nuclear force.


The field that permeates all of space-time and compels many other particles, including electrons, to interact with it is the Higgs boson. These electrons gain mass as a result of that contact. Whatever interacts with the Higgs more,

The W and Z bosons are two of the numerous particles that interact with the Higgs boson, and it is through this interaction that they gain mass. The weak nuclear force's characteristics are determined by the mass of the W and Z bosons because it is those particles that carry out the work.

What determines the mass of every particle that engages in interaction with the Higgs? Why, none other than the Higgs' own mass. All other particles, including the W and Z bosons, would alter if it had a different mass.

 

A visual representation of the 2012 event at CERN's CMS detector in shows the decay characteristic of a Higgs boson into a pair of photons (dashed yellow lines and green towers).  (Image credit: CERN)

This is a good opportunity to mention how strange the Higgs mass is. It is large—about 250 GeV, which is large for particles—but not enormous. It's not small either. In fact, according to a simplistic understanding of how the Higgs functions based on quantum mechanics, all the interactions it is constantly involved in—which are numerous—would either perfectly cancel each other out, reducing its mass to zero, or reinforce one another, increasing it to a point close to infinity.

The Higgs boson is being precisely fine-tuned to a range that is "acceptable" and maintains sanity. However, the W and Z bosons are constrained to their minuscule values by the Higgs boson, allowing the weak nuclear force to be much, much stronger.

In other words, the reason gravity is the weakest force in the cosmos is not that gravity is flawed, but rather that it is "cheating."

There is no agreed-upon solution to the Higgs mass's out-of-the-ordinary state, and as a result, no agreed-upon answer to the hierarchy issue or the strange gravitational weakening.

But all of this discussion is predicated on the assumption that our calculations of the Higgs boson mass, the Planck mass, and other quantities are accurate. Maybe there's something fundamental to the cosmos that we're overlooking.

Among the countless options, some hypotheses cast doubt on our comprehension of the structure of space-time itself. Such concepts are already on the table thanks to string theory, whose math requires the presence of new, tiny spatial dimensions.

A conceptual artistic illustration of string theory.  (Image credit: Getty Images)

However, according to string theory, those extra dimensions are incredibly tiny, twisted up into tiny shapes that are no larger than a Planck length.

However, it's feasible that some of those additional dimensions are slightly larger. Despite the fact that these ideas typically refer to "huge additional dimensions," they are only a millimetre or two in size.

These theories limit the other three forces of nature to our typical, three-dimensional universe, known as a "brane." However, the "bulk," or all the dimensions, allows gravity to reach further. According to this theory, gravity is just as powerful as the other forces, if not stronger, but it must spread out over more dimensions than any other force. Therefore, based on our three-dimensional experiments, it only seems weaker.

We haven't always tested gravity at such tiny scales, but we have measured gravity with great accuracy. We would start to observe strange phenomena at distances of less than a millimetre if our universe had extra "big" spatial dimensions.

For instance, since gravity hasn't had a time to "leak out" to the additional dimensions, we might observe it operating stronger than expected at close ranges. Or, we might begin creating miniature black holes in our particle colliders because doing so would be simpler than we had anticipated.

No experiment has, as of yet, discovered any proof that there are additional dimensions. And gravity is still disappointingly feeble.

Source: Space.com