Pedro Lilienfeld

Second Edition (2026)

Background

At least 35 years ago I started to speculate about the idea that our universe, the one we know about and to which we belong, is only one of many. I was driven to that concept by the extant growing consensus about the Big Bang genesis of the universe. It meant that the universe had not existed forever and, perhaps, will not exist forever into the future. That sudden “creation” of everything at an arbitrary time zero struck me as a potentially teleological concept, contrary to my rationalistic convictions. I further speculated that the idea of a multiverse would fit into my more general view that the entirety of reality consists of a nested infinitude of dimensional hierarchies, ranging from the ultra small to the ultra large.

We, humanity, inhabit an intermediate dimension, between these two —presently accepted — boundaries. Our understanding about these two extremes has been expanding through centuries of scientific advances. Presently, those two limits are represented, at the low end, by the Planck length, considered the smallest length that has physical meaning, and at the upper boundary by the probable diameter of our observable universe; approximately 1.6 x 10^-35 meters and 8.6 x 10²⁶ meters, respectively. Those dimensions correspond to a huge overall span of about 5 x 10⁶¹. That range has been attained within the last two decades, or so. Compare that result with that of the Ancient Greek knowledge that covered an approximate overall range of perhaps no more than 3 x 10¹³,from the smallest grain of sand to the distance to the Sun as calculated by Hipparchus. By the year 1838, when the distance to a star other than the Sun was measured for the first time, and the optical microscope had been in use, that overall span was of the order of a factor of 10²³. By the 1920s, this range had expanded perhaps by another four orders of magnitude, to encompass the Milky Way, then considered the universe at large.

Now, my reasoning goes: Why limit that dimensional range to any arbitrary value? If we follow the intellectual evolution of our concept of universe, we can start with that of Aristoteles, consisting of what we now call our solar system, surrounded by a sphere of stars, all of which centered on the Earth. That concept, with some variants (Ptolemy, Tyco Brahe, etc.)

continued until Copernicus, in 1534, replaced the Earth by the Sun as the center of the universe. So far so good, but not so correct. We must, however, acknowledge that in preceding centuries there were thinkers who started to question the idea of such a constrained universe. Heterodox views were pronounced for example by Grosseteste (c. 1168 – 1253), Oresme (c. 1323 – 1382), Nicolas de Cusa (1401 – 1464) and, subsequently, by Giordano Bruno in 1584, suggesting that the stars themselves could be part of systems external to our solar system. These views, nevertheless, were just speculative and not based on observational evidence.

Starting in the latter part of the 16th century and then stimulated by the advent of the telescope during the 17th, humanity’s perception of the universe broke the Aristotelian constraints and expanded rapidly. It became obvious that the universe was much more than our solar system. Ideas about “island universes” such as those of Kant (1724 – 1804), Laplace (1749 – 1827) became accepted suggesting that the cosmos is far greater than previously thought. Then, with the refining of observational tools, it became incontrovertible that the Milky Way consisted of millions of stars one of which is the Sun. Until as late as the 1920s, however, it was generally believed that the Milky Way constituted the entirety of the universe. That mold was thoroughly broken at that point with Hubble’s (1889 – 1953) observations that resulted in a dramatic expansion of our concept of the universe.

Then, throughout the 20th century and into the 21st, our understanding of the universe, its origin, it’s age and observable dimension, dynamics, structure, etc. underwent a truly remarkable growth. But, are we now suddenly confronted with a conceptual wall?

My Multiverse Reasoning

At the outset I must confess that my reasoning is grounded on thin ice. I do not have anything approaching the theoretical armamentarium nor any access to advanced observational tools to base my ideas. These are merely supported by what I would like to call my personal logic. A profound thinker and outstanding physicist — perhaps the greatest of the late 20th century — Stephen Weinberg, would, justifiably frown upon my approach. He incisively labelled concepts as either “ought to be” or “is”. To the former belong philosophically based hypotheses, e.g., Aristoteles’s concept of the universe, i.e., the Earth “ought to be” the center of the universe, or the idea, prevalent until the late 19th century, that there “ought to be” an aether permeating space. Neither corresponded to reality. By contrast, examples of what “is’: Johannes Kepler’s first law (orbits of planets are elliptical), and Albert Einstein’s special relativity equivalence between energy and mass.

We should, however, reflect on the fact that Weinberg himself could not escape his own initial acceptance of an “ought to be” hypothesis. He stated that “the steady-state theory is philosophically the most attractive theory because it least resembles the account given in Genesis”. He was referring to Fred Hoyle’s view that the universe has existed, and has expanded forever by continuous generation of matter. This theory was displaced by the Big Bang formation of our universe. I am happy to state that, as far back as my teenage years, I embraced the steady-state model for the same reason without knowing about Weinberg’s view.

With the above Weinberg “ought-to-be” caveat very much in mind, I will endeavor to introduce my multiverse thinking.

There are three, nearly independent, reasons why I believe that there are multiple universes:

1. A logical extrapolation of the past history of our evolving comprehension of our universe;
2. The hierarchical structure of reality.
3. The, to me, insurmountable fallacy of believing in a singular, arbitrarily timed, appearance of the universe.

I have expounded above the conceptualization of the universe through time, from the Aristotelian view to our present cosmic understanding. That intellectual expansion from an Earth centered solar system to our 21st century cosmos, to me, more than suggests a further extension, i.e., that of the multiverse. This concept also fits into my multiplicity of nested hierarchies, mentioned above and which I will address below. How dare we suddenly believe that we have reached “the end”? That would be an arbitrary barrier contrary to the evolution of our understanding over the centuries.

The hierarchical structure of the reality that we have become aware of and that has expanded over the centuries, suggests an extrapolation beyond the concept of our singular universe. The concept of hierarchies applies both to the realm of the ultra small as well as the ultra large. As to the former of these, as we descend the ladder from our own dimensional realm we enter the molecular world followed by atoms, atomic nuclei, hadrons (protons and neutrons), followed downwards by quarks which are, at this time, not known to be made of anything smaller although string theory may suggest otherwise. A corresponding hierarchical sequence of the macroscopic world would be constituted by planets, solar systems, galaxies, galactic groupings, galactic clusters and superclusters, and finally our universe. So, Why stop here?

I do not pretend to define and characterize that multiverse whose existence I have postulated by the preceding intellectual extrapolation. I am simply justifying it’s existence by a logical extension of the history of knowledge.

Now, to the third argument. It is, to me, even more persuasive that the first two. The concept that the universe suddenly appeared at an arbitrary time zero, not having existed before, stretches my imagination to the breaking point. Why not later? Why at all, indeed? Such, quasi capricious sudden occurrence in time almost suggests a divine intervention. Even the notable Catholic churchman/astronomer Georges Lemaître cautioned the Vatican not to interpreted the Big Bang as a confirmation of an act of divine creation. So, why would the universe just appear out of nowhere at that particular moment? It would have been more acceptable if the Trinity nuclear test explosion in the Nevada desert would have gone off by itself, without having been triggered by an operator.

Such unlikely and temporarily arbitrary happening strongly suggests, to me, that the Big Bang was merely one event among uncountable events of that type, in some way interconnected and interdependent. Perhaps as popping bubbles in an immense multiverse cauldron. However, that image should be treated with caution, being merely an imaginary and anthropomorphic construct.

Thus, the idea that the universe suddenly came “out of the blue” seems to me entirely contrived and unlikely.

Views of the Scientific Community

The idea of the multiverse can be traced back many centuries, evento Greek Antiquity. Those flights of fantasy, although historically interesting are inconsequential because they squarely belong to the “ought to be” category of speculation. So does an opinion by Winston Churchill illustrate a purely personal view:

“Certainly nothing could be more repulsive to both our minds and feelings than the spectacle of thousands of millions of universes – for that is what they say it comes to now – all knocking about together for ever without any rational or good purpose behind them”.

I will limit here to what modern science has to adduce on this subject. That modern contribution will be restricted to the latest hypotheses derived from what is being gleaned in the last three decades, or so, from cosmological observations and related theoretical considerations.

In essence, it must be stated that there is, at present, no scientific consensus as to the existence of the multiverse. There are, in fact, two opposing parties on the matter: proponents and skeptics.

Wikipedia cites: “The concept of multiple universes, or a multiverse, has been discussed throughout history. It has evolved and has been debated in various fields, including cosmology, physics, and philosophy. Some physicists have argued that the multiverse is a philosophical notion rather than a scientific hypothesis, as it cannot be empirically falsified. In recent years, there have been proponents and skeptics of multiverse theories within the physics community. Although some scientists have analyzed data in search of evidence for other universes, no statistically significant evidence has been found. Critics argue that the multiverse concept lacks testability and falsifiability, which are essential for scientific inquiry, and that it raises unresolved metaphysical issues.

Max Tegmark and Brian Greene have proposed different classification schemes for multiverses and universes. Tegmark’s four-level classification consists of Level I: an extension of our universe, Level II: universes with different physical constants, Level III: many-worlds interpretation of quantum mechanics, and Level IV: ultimate ensemble. Brian Greene’s nine types of multiverses include quilted, inflationary, brane, cyclic, landscape, quantum, holographic, simulated, and ultimate. The ideas explore various dimensions of space, physical laws, and mathematical structures to explain the existence and interactions of multiple universes. Some other multiverse concepts include twin-world models, cyclic theories, M-theory, and black-hole cosmology.

The anthropic principle suggests that the existence of a multitude of universes, each with different physical laws, could explain the asserted appearance of fine-tuning of our own universe for conscious life. The weak anthropic principle posits that we exist in one of the few universes that support life. Debates around Occam’s razor and the simplicity of the multiverse versus a single universe arise, with proponents like Max Tegmark arguing that the multiverse is simpler and more elegant. The many-worlds interpretation of quantum mechanics and modal realism, the belief that all possible worlds exist and are as real as our world, are also subjects of debate in the context of the anthropic principle”.

Modern proponents of one or more of the multiverse hypotheses include Lee Smolin, Don Page, Brian Greene, Max Tegmark, Alan Guth, Andrei Linde, Michio Kaku, David Deutsch, Leonard Susskind, Alexander Vilenkin, Yasunori Nomura, Raj Pathria, Laura Mersini-Houghton, Neil deGrasse Tyson, Sean Carroll and Stephen Hawking.

Scientists who are generally skeptical of the multiverse hypothesis include David Gross, Paul Steinhardt, Anna Ijjas, Abraham Loeb, David Spergel, Neil Turok, Viatcheslav Mukhanov, Michael S. Turner, Roger Penrose, George Ellis, Joe Silk, Carlo Rovelli, Adam Frank, Marcelo Gleiser, Jim Baggott and Paul Davies.

Obviously, I align myself with the former group. I also consider the supporters of the possibility of the multiverse, listed above, as being, in general, more authoritative than the skeptics.

Summarizing, the concept of the multiverse, although not confirmed by observation, is very much part of the scientific discourse. The great challenge is to prove its reality which demands a rigorous proof. It is the ultimate test of Pierre Simon Laplace’s dictum: “Le poids des preuves pour une affirmation extraordinaire doit être proportionné à son étrangeté” (The weight of evidence for an extraordinary claim must be proportioned to its strangeness).