What Came Before The Big Bang? | Niayesh Afshordi | AFP 53

The following is based on a conversation with Niayesh Afshordi, a Professor of physics and astronomy at the University of Waterloo, and research associate faculty in astrophysics at Perimeter Institute.

What is the Hawking-Penrose Singularity, and why does it signal a limitation in standard physics?

The Hawking-Penrose singularity theorems mathematically demonstrated that under general relativity, an expanding universe traced backward in time must collapse into a point of infinite density and infinite curvature, a singularity where time itself effectively stops. However, physicists view this singularity not as a physical reality, but as a boundary where general relativity breaks down because it fails to incorporate quantum mechanics. It represents the limit where our current equations cease to be valid rather than a literal creation event.

What is Cosmic Inflation, and how does it solve the “Horizon Problem”?

Cosmic inflation is a theory proposing that the very early universe underwent a period of rapid, exponential expansion. It addresses the “Horizon Problem”, the puzzle of why opposite sides of the observable universe share the exact same temperature in the Cosmic Microwave Background (CMB) despite being too far apart for light or information to have traveled between them. Inflation posits that these regions were once extremely close together and in thermal equilibrium before being rapidly stretched apart by space expanding faster than the speed of light. This rapid expansion also magnified subatomic quantum fluctuations into the primordial sound waves that seeded the universe’s large-scale structure.

What did the Copenhagen and American Physical Society surveys reveal about modern scientific consensus on the Big Bang?

Surveys conducted among professional physicists, including one at a conference in Copenhagen and a broader survey by the American Physical Society, revealed that 68% of respondents agree on a redefined concept of the Big Bang. Instead of viewing it as the singular “beginning of time,” the majority definition describes the Big Bang simply as an early epoch when the universe was extremely dense and hot. Beyond this baseline definition, the surveys showed very little consensus on fundamental issues like quantum gravity or pre-Big Bang models, demonstrating that foundational cosmology remains an open, evolving field.

Cleaned Transcript

Jeroen Schreel: Welcome to Apple Finch Pudding, your gateway to the world of science. Today’s guest is Niayesh Afshordi, a professor of physics and astronomy at the University of Waterloo and research associate faculty at the Perimeter Institute. His work ranges from astrophysics and cosmology to fundamental physics. Niayesh is also known as the author of the book Battle of the Big Bang. Welcome, Niayesh.

Niayesh Afshordi: It’s great to be here. Thank you for having me.

Jeroen Schreel: Before we delve more into astrophysics and the Big Bang, do you have a fun science fact for our listeners?

Niayesh Afshordi: Yeah, I think the fun science fact is that the Big Bang is not what we thought it is. Everybody thinks everything started with the Big Bang, but as we’ll get into, everything doesn’t necessarily start with the Big Bang.

Jeroen Schreel: You’re already stealing my questions, but it’s perfect! I love it. It’s also something you mention in your book. If I’m not mistaken, you state that while we can agree a Big Bang happened, we don’t all agree on what the Big Bang actually is. Could you explain what the Big Bang really is?

Niayesh Afshordi: Yeah, we managed to come up with an analogy for it. The story of our book was interesting because I collaborated with a co-author, Phil, who is very passionate about astronomy, though that wasn’t his original background—he used to be a banker before getting bored with making money. He got back into his passion, astronomy, and realized the best way to understand things was to interview scientists. He became a YouTuber, an amateur astronomer, and a very good science communicator.

Through our discussions—because scientists get so deep in their fields that they can lose sight of the big picture—working with Phil helped us reframe what the Big Bang actually means.

Beyond the popular cartoon version where everything starts with a Big Bang, we’ve learned over the years to evaluate what physics is missing versus what physics we do understand. We can never know everything for sure; we make assumptions, observe, and adjust our assumptions based on new observations and logical deduction. Sometimes assumptions are inconsistent when placed together. You may want to read a lot and also exercise a lot, but at some level, doing both to an extreme is inconsistent within a single day.

Jeroen Schreel: To be honest, I’ve tried to read and stay fit—it really is a balance!

Niayesh Afshordi: You have to experimentally find where that balance is. If you set goals too high, you realize they don’t fit together in the time you have. That is how the science of the Big Bang has evolved.

Science had a huge leap in the early 20th century with the discoveries of quantum mechanics on one hand and relativity—how space, time, and gravity work together—on the other. We used those frameworks to interpret observations and reconstruct cosmic history. We look at the sky, see that the universe is expanding, and realize that turning back the clock brings galaxies closer together, making conditions hotter.

Based on that, Stephen Hawking and Roger Penrose famously proved theorems showing that standard general relativity, traced backward, leads to a point of infinite density and infinite curvature—a singularity where clocks stop ticking. But just like trying to read 10 books and run a marathon every day, this was where the math hit a limit.

The term “Big Bang” was actually coined by Fred Hoyle, a famous British astrophysicist who was a critic of the picture. The issue is that the underlying classical assumptions don’t have to be entirely correct.

A better analogy is waking up from a dream. When you wake up, you remember seeing the light or checking the clock at 6:00 AM, but what happened before that is fuzzy. The story of the Big Bang is the story of waking up from a cosmic dream. Using our collective observations, we piece together relics to perform archaeology back to a certain point. Before that point, we lack the tools to directly remember.

That is the modern scientific definition of the Big Bang: a boundary beyond which we cannot currently observe what happened. It doesn’t mean you can’t theorize—people in the same room can wake up to the same reality after having very different dreams. Different theories for what came before must be supported by evidence and be self-consistent. The rules under those extreme initial conditions could have been fundamentally different, continuously evolving into the well-tested physical laws we observe today in particle accelerators and black hole observations.

Jeroen Schreel: If we traveled back in a time machine toward the Big Bang, what would we observe?

Niayesh Afshordi: Going back a few billion years, you’d need an oxygen mask because atmospheric oxygen only accumulated after photosynthesis evolved. Beyond 5 billion years ago, the Earth and solar system hadn’t formed yet.

Further back, you would see a younger, smaller galaxy forming from mergers. Eventually, there are far fewer stars and planets because heavier elements—what astronomers call “metals” (anything heavier than hydrogen and helium)—hadn’t been forged inside stars yet.

Continuing backward, the universe becomes hotter and less structured. Instead of stars and planets, it is a uniform, three-dimensional sea of plasma and photons with propagating waves. The “bang” in Big Bang is appropriate here: these are primordial sound waves that moved through the early plasma. They are the direct probes of the early universe, eventually freezing and growing under gravity to form galaxies, stars, and planets.

Jeroen Schreel: Are those sound waves the same thing as the Cosmic Microwave Background radiation?

Niayesh Afshordi: The Cosmic Microwave Background (CMB) is the light emitted by that hot plasma. Early on, the universe was dense and opaque. When the density dropped—around 400,000 years after the Big Bang (the surface of last scattering)—photons began traveling freely. As the universe expanded, that light stretched from high-energy radiation down to microwave wavelengths.

While the microwaves themselves are light, mapping their tiny temperature variations across the sky gives us a snapshot of those primordial sound waves as they existed 400,000 years after the Big Bang.

Jeroen Schreel: How do those microwaves help us reconstruct what happened in the past?

Niayesh Afshordi: Experiments like NASA’s WMAP and the European Space Agency’s Planck satellite mapped these temperature fluctuations across the sky. By analyzing the statistics of these spots across different angular scales, we get an oscillating pattern that can be fitted using cosmological models with just five or six parameters.

These parameters reveal the universe’s overall density, as well as the proportions of radiation, dark matter, and ordinary matter. Longer wavelengths haven’t had time to oscillate much, reflecting conditions closer to the Big Bang, while shorter wavelengths oscillated rapidly. By factoring out these oscillations, we can infer the original spectrum and volume of the sound waves at the Big Bang to determine what mechanism generated them. The leading explanation is Cosmic Inflation.

Jeroen Schreel: What is inflation?

Niayesh Afshordi: It has nothing to do with financial inflation!

In standard Big Bang cosmology, there was a puzzle called the Horizon Problem. The CMB has a nearly uniform temperature (~2.7 Kelvin) in every direction. Under standard expansion, distant regions of space wouldn’t have had enough time since the Big Bang to exchange light and equalize their temperatures.

Cosmic Inflation proposes that the early universe was initially tiny, allowing all regions to communicate and reach a uniform temperature. Then, a brief period of exponential expansion occurred, doubling the size of space roughly 100 times in a fraction of a second. This magnified subatomic quantum fluctuations into macro-scale density ripples, generating the sound waves we observe today. In modern cosmology, inflation is viewed as a pre-Big Bang state that preceded the hot, expanding phase.

Jeroen Schreel: Could you share some alternative theories about what happened before the Big Bang?

Niayesh Afshordi: Beyond light and sound waves, we hope to observe primordial gravitational waves—ripples in space-time geometry predicted by Einstein’s general relativity. Because space was extremely dense early on, energetic processes could have generated gravitational waves that travel unimpeded.

About 10 years ago, there was excitement over a potential detection via CMB polarization (the BICEP2 experiment), but that signal turned out to be Galactic dust. Detecting primordial gravitational waves remains a primary goal, as different pre-Big Bang models predict different gravitational wave signatures.

High-energy inflation models predict significant gravitational wave production, whereas lower-energy models predict very little. A major criticism of inflation is that there are many variants, making the overall paradigm difficult to falsify.

Alternatives include:

• Varying Speed of Light (VSL) models: Models where the speed of light was significantly faster in the early universe, solving the Horizon Problem without requiring exponential expansion. These models predict distinct statistical signatures in the sound waves and negligible gravitational waves.

• Bouncing Cosmologies: Models where an earlier universe collapsed to a high density before bouncing back into an expansion phase.

Jeroen Schreel: What does the “Big Bounce” mean? Is it a cyclical contracting and expanding universe?

Niayesh Afshordi: That is one variation. There are non-cyclical bounces, such as a model I worked on where a four-dimensional star collapses in a five-dimensional space-time to form a black hole, extruding our three-dimensional universe as an expanding membrane.

Alternatively, Roger Penrose proposed Conformal Cyclic Cosmology (CCC). In CCC, there is no physical collapse or bounce; instead, in the far future, an expanding universe loses massive particles and “forgets” its physical scale. Mathematically, an infinitely large, cold universe becomes identical to an infinitely small, hot Big Bang, initiating the next cycle.

Jeroen Schreel: In your 4D star collapse model, does that mean we live inside or came out of a black hole?

Niayesh Afshordi: We would emerge from it. The appeal comes from the “No-Hair Theorem,” which dictates that regardless of how complex a collapsing star is, the resulting black hole is described simply by its mass and angular momentum. This simplicity could explain why our early universe was so uniform. In that scenario, a quantum process ejects a 3D membrane out of the 4D black hole’s horizon. However, detailed calculations showed its predictions for the CMB sound waves didn’t match observational data perfectly. As Richard Feynman said, “Science is imagination in a straightjacket”—ideas must fit the data.

Jeroen Schreel: Do these models imply the existence of a Multiverse?

Niayesh Afshordi: The concept of the multiverse emerged from the convergence of three ideas:

1. Eternal Inflation: Quantum fluctuations during inflation can cause certain regions to continue inflating exponentially forever, spawning isolated “bubble” universes with different properties.

2. String Theory: The leading candidate for quantum gravity requires extra dimensions and yields a vast “landscape” of possible physical vacuum states rather than a single unique prediction.

3. The Many-Worlds Interpretation of Quantum Mechanics: The idea that all probabilistic quantum outcomes physically occur across parallel branches.

The main issue with the multiverse is testability. If a theory cannot be falsified, it risks stepping outside empirical science. There are potential observational signatures, such as searching for collisions between our bubble universe and adjacent ones in the CMB. However, these predictions suffer from the “measure problem”: defining meaningful probabilities in an infinite universe is mathematically ill-defined.

Jeroen Schreel: You recently conducted a survey in Copenhagen asking physicists about foundational problems. What were the results?

Niayesh Afshordi: My co-author Phil Hopper and I surveyed roughly 100 physicists at a conference, and we followed up with a larger survey through the American Physical Society with nearly 1,700 respondents.

The most striking finding was that 68% of respondents in both surveys agreed on the definition of the Big Bang: it simply means the early universe was much denser and hotter, without implying a singularity or a definitive beginning of time.

On almost every other foundational question—such as the nature of quantum gravity, black hole evaporation, or pre-Big Bang origins—there was no broad consensus. String theory, for instance, received only 20–30% support as the leading theory of quantum gravity. This highlights that foundational physics remains wide open.

Jeroen Schreel: Have you ever changed your mind about a theory you previously believed?

Niayesh Afshordi: Constantly! Max Planck famously noted that “science advances one funeral at a time” because scientists often struggle to abandon their own models. But as experimental data improves, models get ruled out. Many specific inflationary models and pre-Big Bang scenarios I’ve analyzed have been ruled out or put under strong statistical tension by CMB data.

Jeroen Schreel: What major breakthroughs do you foresee in the near future?

Niayesh Afshordi: Higher-precision cosmological maps from ground observatories like the Simons Observatory and space missions like Euclid, SPHEREx, Rubin, and Roman will further constrain early universe models.

Looking further ahead, space-based laser interferometers such as LISA and the proposed Big Bang Observer aim to detect primordial gravitational waves directly by measuring distance variations between satellites with extreme precision.

Jeroen Schreel: Do you have a final take-home message for our listeners?

Niayesh Afshordi: To follow science, you have to embrace uncertainty. Uncertainty is not a bug; it’s a feature that allows imagination to thrive. We must apply the scientific method to test that imagination against reality. If everyone embraced uncertainty and applied the scientific method in daily life, the world would be a better place.

Jeroen Schreel: That is a wonderful note to end on. Thank you, Niayesh Afshordi.