As far as we can measure, the laws of physics have not changed over the 13.8-billion-year history of the universe. The fundamental constants that govern gravity, electromagnetism, and nuclear forces appear to be the same today as they were when the first atoms formed. But “as far as we can measure” is doing a lot of work in that sentence. Several lines of evidence hint that change is not impossible, and some theoretical frameworks actually predict it.
What “Laws of Physics” Actually Means Here
When physicists ask whether the laws of physics can change, they’re really asking about two related things. The first is the mathematical relationships themselves: does gravity still follow an inverse-square law, does energy still convert to mass the way Einstein described? The second is the fundamental constants embedded in those equations: the speed of light, the strength of gravity, the charge of an electron. A shift in either one would change how the universe behaves.
Most research focuses on the constants, because they’re measurable. If the strength of the electromagnetic force were even slightly different billions of years ago, it would leave fingerprints in the light from ancient quasars. That makes them a practical way to test whether the universe’s rulebook has been rewritten over time.
What Measurements Show So Far
The most precisely tested constant is the fine-structure constant, often called alpha, which determines how strongly charged particles interact with light. Astronomers can measure its value billions of years in the past by analyzing how ancient gas clouds absorbed light from distant quasars. Each element leaves a characteristic pattern of absorption lines, and the spacing of those lines depends on alpha’s value at the time.
In 2020, a team used the x-shooter spectrograph on the Very Large Telescope to take four direct measurements of alpha from roughly 13 billion years ago, when the universe was less than a billion years old. The weighted average deviation from today’s value was just negative 2.18 parts per hundred thousand, plus or minus 7.27. That margin of error swallows the deviation entirely, meaning the result is consistent with zero change.
The gravitational constant, G, is harder to pin down because gravity is so much weaker than the other forces. The tightest experimental bounds on its rate of change come from observations of compact binary star systems spiraling toward each other. These constrain any drift in G to less than about 7 parts per billion per year. For practical purposes, gravity’s strength is holding steady.
The Hints That Something Might Vary
Not every measurement comes back clean. A large analysis of 293 quasar measurements found something unexpected: alpha might not just vary over time but across space. The data fit a dipole pattern, meaning the electromagnetic force appears very slightly stronger in one direction of the sky and very slightly weaker in the opposite direction. The amplitude of this variation is about 8.1 parts per million, and the statistical preference for a nonzero signal sits above the four-sigma level, which is notable but not yet at the five-sigma threshold physicists typically require to claim a discovery.
This remains controversial. The signal could reflect subtle differences between the telescopes and instruments used to gather data from different parts of the sky. But if confirmed, it would mean the fine-structure constant isn’t truly universal. It would be close to the same everywhere, differing by only a few millionths of a percent, but not identical.
How the Laws Were Different at the Very Beginning
The strongest case for the laws of physics being “different” comes from the earliest moments of the universe. In the first fraction of a second after the Big Bang, the universe was so hot and dense that the four fundamental forces (gravity, electromagnetism, the strong nuclear force, and the weak nuclear force) were unified into fewer distinct forces, possibly a single one. All particles were massless. Spacetime itself was a chaotic foam.
As the universe expanded and cooled, it underwent a series of phase transitions, somewhat like water freezing into ice. At each transition, a force “broke away” from the others. The separation of gravity from the other forces created recognizable spacetime. The later split between the strong force and the electroweak force released enough energy to drive a brief period of exponential expansion called inflation. Eventually the electromagnetic and weak forces separated, giving particles their distinct masses.
So in a very real sense, the laws of physics as we experience them are the product of cooling. The underlying equations may have been the same throughout, but the way they played out looked radically different when the universe was a trillionth of a second old compared to today. The physics of everyday life, the chemistry that makes stars burn and molecules bond, only became possible after these transitions were complete.
Theories That Predict Changing Constants
Several serious theoretical frameworks allow for constants to vary. The idea actually traces back to Einstein himself. In 1911, he published papers exploring the possibility that the speed of light could vary from place to place under the influence of gravity. He argued that while local experiments (like the famous Michelson-Morley experiment) would always measure the same speed of light, the value need not be the same everywhere in the universe.
Modern versions of this idea connect the speed of light and Planck’s constant to a dynamic field that can change across spacetime. One recent model ties both quantities to the same field that gives particles their mass through the Higgs mechanism. In this framework, the speed of light and the quantum of action both shift as the field’s value changes from point to point. The practical consequence is striking: if the speed of light has been slowly declining over cosmic time, it could explain the accelerating expansion of the universe without needing dark energy at all. It could also resolve the persistent disagreement between different methods of measuring the universe’s expansion rate.
String theory offers a different route to varying laws. In string theory, the familiar three dimensions of space are accompanied by additional tiny dimensions, curled up too small to observe directly. The shape and size of these extra dimensions determine which particles exist, how strong the forces are, and what masses particles carry. String theory’s equations allow an enormous number of possible shapes for these dimensions, each producing a different set of physical laws. If different regions of the universe settled into different configurations during the rapid expansion after the Big Bang, then the “laws of physics” in those regions would genuinely differ from ours. The particles, forces, and constants would all be different, not because the underlying theory changed, but because the geometry did.
Why Even Tiny Changes Would Matter
The constants of nature appear to be finely balanced for the existence of complex structures. Change the electromagnetic force by a small amount and atoms behave differently. Change gravity and stars burn at different rates or fail to form at all. But the relationship is subtler than it first appears.
Researchers have found that you can change multiple constants simultaneously in ways that keep stars and heavy elements intact. The catch is that other properties of matter shift in unexpected ways. For example, certain combinations of altered constants would leave stellar physics untouched but make all fluids at least as viscous as tar, which would make biology as we know it impossible. The universe wouldn’t look broken from the outside. Stars would shine, planets would orbit. But nothing would be alive to notice.
This sensitivity cuts both ways. It means the constants don’t need to change much to have profound effects, but it also means there may be more room for variation than the simplest “fine-tuning” arguments suggest. The question isn’t just whether a single constant can shift, but how the whole web of constants moves together.
The Short Answer
The laws of physics have been remarkably stable for at least 13 billion years, with no confirmed variation in any fundamental constant beyond measurement uncertainty. But “stable” is not the same as “fixed forever by decree.” The early universe operated under effectively different rules before the forces separated. Credible theoretical models allow constants to vary, and at least one intriguing dataset hints at a tiny spatial variation in the electromagnetic force across the sky. The most honest summary is that the laws of physics appear constant to extraordinary precision, but physics itself does not guarantee they must be.