Most physicists believe that the structure of spacetime is formed in an unknown way at the Planck scale, i.e., at a scale close to one trillionth of a trillionth of a metre. However, careful considerations undermine this prediction. There are quite a few arguments in favour of the emergence of spacetime as a result of processes taking place at the level of quarks and their conglomerates.

What is spacetime? The absolute, unchanging arena of events? Or perhaps it is a dynamic creation, emerging in some way on a certain scale of distance, time or energy. References to the absolute are not welcome in today's physics. It is widely believed that spacetime is emergent. It is not clear, however, where the process of its emergence takes place. The majority of physicists tend to suppose that spacetime is created on the Planck scale, at distances close to one trillionth of a trillionth of a metre (~10-35 m). In his article in *Foundations of Science*, Professor Piotr Zenczykowski from the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN) in Cracow systematizes the observations of many authors on the formation of spacetime, and argues that the hypothesis about its formation at the scale of quarks and hadrons (or quark aggregates) is quite sensible for a number of reasons.

Questions about the nature of space and time have puzzled humanity since at least antiquity. Are space and time separated from matter, creating a "container" for motions and events occurring with the participation of particles, as Democrit proposed in the 5th century BC? Or perhaps they are attributes of matter and could not exist without it, as Aristotle suggested a century later? Despite the passage of millennia, these issues have not been resolved yet. Moreover, both approaches, though contradictory, are deeply ingrained into the pillars of modern physics.

In quantum mechanics, events take place in a rigid arena with uniformly flowing time. Meanwhile, in the general theory of relativity, matter deforms elastic spacetime (stretching and twisting it), and spacetime tells particles how to move. In other words, in one theory, the actors enter an already prepared stage to play their roles, while in the other, they create the scenography during the performance, which in turn influences their behaviour.

In 1899, German physicist Max Planck noticed that with certain combinations of some constants of nature, very fundamental units of measurement could be obtained. Only three constants—the speed of light c, the gravitational constant G and Planck's constant h—were sufficient to create units of distance, time and mass, equal (respectively) to 1.62 · 10^{-35} m, 5.39 · 10^{-44} s and 2.18 · 10^{-5} g. According to today's mainstream belief, spacetime would be created at Planck's length. In fact, there are no substantive arguments for the rationality of this hypothesis.

Both our most sophisticated experiments and theoretical descriptions reach the scale of quarks, i.e., the level of 10^{-18} m. So how do we know that along the way to Planck's length—over a dozen consecutive, ever smaller orders of magnitude—spacetime retains its structure? In fact, we are not even sure if the concept of spacetime is rational at the level of hadrons! Divisions cannot be carried out indefinitely, because at some stage the question of the next smaller part simply ceases to make sense. A perfect example here is temperature. This concept works very well on a macro scale, but when, after subsequent divisions of matter, we reach the scale of individual particles, it loses its raison d'etre.

"At present, we first seek to construct a quantized, discrete spacetime, and then 'populate' it with discrete matter. However, if spacetime were a product of quarks and hadrons, the dependence would be reversed—the discrete character of matter should then enforce the discreteness of spacetime," says Prof. Zenczykowski. "Planck was guided by mathematics. He wanted to create units from the fewest constants possible. But mathematics is one thing, and the relationship with the real world is another. For example, the value of Planck's mass seems suspicious. One would expect it to have a value rather more characteristic for the world of quanta. In the meantime, it corresponds to approximately one-tenth of the mass of a flea, which is most certainly a classical object."

Since we want to describe the physical world, we should lean toward physical rather than mathematical arguments. So when using Einstein's equations, we describe the universe at large scales, and it becomes necessary to introduce an additional gravitational constant, known as the cosmological constant Lambda. Therefore, while constructing fundamental units, if we expand the original set of three constants by Lambda, in the case of masses, we obtain not one but three fundamental values: 1.39 · 10^{-65} g, 2.14 · 10^{56} g, and 0.35 · 10^{-24} g. The first of these could be interpreted as a quantum of mass, the second is at the level of the mass of the observable universe, and the third is similar to the masses of hadrons (for example, the mass of a neutron is 1.67 · 10^{-24} g). Similarly, after taking Lambda into account, a unit of distance of 6.37 · 10-^{15} m appears, very close to the size of hadrons.

"Playing games with constants, however, can be risky, because a lot depends on which constants we choose. For example, if spacetime was indeed a product of quarks and hadrons, then its properties, including the velocity of light, should also be emergent. This means that the velocity of light should not be among the basic constants," says Prof. Zenczykowski.

Another factor in favour of the formation of spacetime at the scale of quarks and hadrons are the properties of the elementary particles themselves. For example, the Standard Model does not explain why there are three generations of particles, where their masses come from, or why there are so-called internal quantum numbers, which include isospin, hypercharge and colour. In the picture presented by Prof. Zenczykowski, these values can be linked to a certain six-dimensional space created by the positions of particles and their momenta. The space thus constructed assigns the same importance to the positions of particles (matter) and their movements (processes). It turns out that the properties of masses or internal quantum numbers can then be a consequence of the algebraic properties of 6-D space. What's more, these properties would also explain the inability to observe free quarks.

"The emergence of spacetime may be associated with changes in the organization of matter occurring at a scale of quarks and hadrons in the more primary, six-dimensional phase space. However, it is not very clear what to do next with this picture. Each subsequent step would require going beyond what we know. And we do not even know the rules of the game that nature is playing with us—we still have to guess them. However, it seems very reasonable that all constructions begin with matter, because it is something physical and experimentally available. In this approach, spacetime would only be our idealization of relations among elements of matter," says Prof. Zenczykowski.

**Explore further:**
Hunting for dark quarks

**More information:**
Piotr Żenczykowski, Quarks, Hadrons, and Emergent Spacetime, *Foundations of Science* (2018). DOI: 10.1007/s10699-018-9562-2

## Doug_Nightmare

In infinite Time, and in hypothetical infinite space, everything that can happen must happen and infinitely many times.

## RobertKarlStonjek

We are reminded of the planetary system of the electron around the nucleus and the ancient idea of the atom as an indestructible solid and undivided substrate of reality. The same idea was repeated in modern times with string theory where theorists imagine that all you need is geometry and the little strings can explain the rest.

The theorists in this article imagine Planck scale quantums of space will do it, but they would not fit into a singularity for starters.

The correct and incontrovertible answer is 'we don't know', but where's the fun in that. Science will speculate until a method of actually probing the next smallest scale is discovered and all our theories are blown away once more...

## rrwillsj

And the Simplistic Model which approximates an atom as sort like a model Solar System. This simplified version is generally what is taught to school children. As a model they can imagine.

Unfortunately, many, maybe most people, never get taught the Advanced Model with all it's difficult complexity.

These models are like the steps pn a ladder. A lot of people stop short. Unwilling or unable, to take the risks and make the laborious effort to continue climbing.

## KBK

## julianpenrod

An example, Maxwell said light is composed of two mutually coordinated, disembodied, oscillating electrostatic and magnetic fields. As the electrostatic field oscillates, it gives rise to the oscillating magnetic field. As the oscillating magnetic field oscillates, it gives rise to the oscillating electromagnetic field that gives rise to the oscillating magnetic field. Neither has an independent existence one gives rise to the other, which gives rise to the first, and so on.

## julianpenrod

Note that it is still reported that there are seasonal variations of the observed speed of light of Michelson-Morley Apparatus, but they aren't generally mentioned.

## Da Schneib

## julianpenrod

It should be mentioned, though, it is said radioactive decay rates change with the seasons. Implying orientation in space alters the rates. Just as light supposedly should change its speed with respect to direction of travel in spacer. Rates of decay are like a clock, suggesting time changes with direction in space.

## julianpenrod

## julianpenrod

I have pointed this out repeatedly but been dismissed.

Throw a ball in the air and the formula describes a parabola that goes downward all the way to infinity. In reality, hitting the ground when coming down will stop it!

Einstein's claim that matter is energy is based only on the fact that "relativistic" kinetic energy is a term minus the product of m and c^2. Einstein" interpreted this to mean energy at zero velocity of mc^2. It could also be said that mc^2 has meaning only as the initial point from which kinetic energy is calculated.

## torbjorn_b_g_larsson

But the key point is that no one need to claim that spacetime emerges at Planck scales. The observation is that a particle of that energy would make a black hole and that leads to a breakdown of understood physics. This also explains the ubiquity of the Planck constant in particle models.

The cosmology is baloney too. Lambda is not primarily a "gravitational" constant, it is the vacuum energy so more related to quantum field theory than to space as such; though of course the GR LCDM cosmology ties these things together.

Not surprisingly IMO Foundations of Science is a non-quality Springer journal where authors can say anything as long as they supply own "reviewers". It has an impact factor < 1 [ https://www.resea..._Science ] - few see any value in its articles in general. YMMV of course.

## torbjorn_b_g_larsson

Not really, since we have one, and it plays nice with the large scale flat space of LCDM cosmology. It is the linearized gravity that goes into Core Theory and makes everything approximated by quantum fields. I note that with the latest Planck data release suggesting a non-Planckian slow roll inflation it is possible that "fields all the way down" is a good approximation of the universe on all scales outside of black holes and ignoring gravity nonlinearities (such as we need to consider in GPS).

I dunno what gravitational nonlinearities arise from. Now QED was secretly a part of electroweak theory and that a part of SM theory, so maybe something similar happens with gravity. But I would like to call it something else than "quantum gravity" - been there, done that.