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On the detection of absolute velocity in a Newtonian universe

This paper challenges the long-held belief that absolute velocity is undetectable in a Newtonian universe by demonstrating that standard arguments supporting this claim are circular, thereby concluding that there are no formal reasons to rule out its detection.

Original authors: Jorge Manero, Ricardo Muciño, Elias Okon

Published 2026-07-21

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Jorge Manero, Ricardo Muciño, Elias Okon

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Great Cosmic Speed Trap

Imagine you are floating in a vast, empty ocean, surrounded by nothing but water and your own boat. If you look out and see another boat drifting nearby, you can easily tell how fast that boat is moving relative to yours. You can measure the distance between you and see it change. This is what we call relative velocity—speed measured against something else. But what if you wanted to know how fast your boat is moving through the water itself, independent of any other boat? In the old days of physics, specifically in the universe described by Isaac Newton, scientists believed there was a hidden, invisible grid called absolute space that filled the entire cosmos. This grid was like a giant, unmoving stage upon which the drama of the universe played out. According to this view, every object had a true, "absolute" speed relative to this invisible stage, not just a speed relative to its neighbors.

For centuries, the big question was: Can we actually find this absolute speed? The standard answer, passed down from Newton himself, was a firm "No." The logic went like this: Since all the forces we can measure (like gravity or collisions) only care about how things move relative to each other, there's no way to tell if the whole universe is drifting slowly across the invisible stage or standing still. It was thought to be a fundamental rule of the universe that absolute speed was a secret the cosmos kept from us. But what if that rule wasn't a law of nature, but just a mistake in how we were asking the question?

The Paper's Big Twist

In this paper, Jorge Manero, Ricardo Muciño, and Elias Okon from the Universidad Nacional Autónoma de México take a fresh look at this old puzzle. They aren't trying to prove that we can find absolute speed in our real, modern universe (because we know our universe isn't actually Newtonian). Instead, they are playing a game of "what if" inside a purely theoretical Newtonian universe to see if the old arguments against finding absolute speed actually hold up.

The authors argue that the standard reasons for believing absolute speed is undetectable are actually circular. It's like saying, "You can't find the hidden treasure because the map only shows things you can already see." They point out that the old arguments assume, right from the start, that only things that stay the same when you shift the whole universe (like relative distances) can be measured. But the paper suggests there is no formal reason in Newton's laws to make that assumption.

To understand their point, imagine two friends, Sally and Harry, in a Newtonian world. The old argument says that if Sally tries to measure her absolute speed and tell Harry, she can't do it because the "message" she sends (like a letter) is made of relative things (ink on paper, which doesn't change if the whole room moves). Therefore, the message can't carry the secret of her absolute speed. The authors say this reasoning is flawed. They argue that just because the message is relative doesn't mean the result of the measurement has to be relative.

Here is the playful analogy they use: Imagine you have a machine that measures the speed of a passing car. In a Newtonian universe, if you bump the car into your machine, the machine's final speed will change based on the car's initial speed. Even if the "bump" only cares about how fast they are moving relative to each other, the machine's final absolute speed (its speed relative to the invisible stage) will end up being a perfect record of the car's initial absolute speed. The machine doesn't need to "know" about the invisible stage; it just needs to react to the collision. The final speed of the machine is the measurement.

The authors show that in a Newtonian universe, you can set up a perfectly valid experiment where the final state of a measuring device (like a bouncing ball or a spinning wheel) encodes the initial absolute speed of the object it hit. The math works out perfectly. The only reason we think we can't do this is because we've arbitrarily decided that a "measurement" must be recorded in a way that ignores absolute speed. But the paper argues that this is just a rule we made up, not a rule written in the laws of physics.

So, what is the verdict? The paper concludes that there are no formal reasons within Newton's own theory to say that absolute velocity is undetectable. The famous claim that it is impossible is based on a logical loop, not a hard fact. The authors are careful to say they haven't proven that absolute speed is detectable in our real world (because our world doesn't follow Newton's rules exactly), but they have proven that the old arguments claiming it must be undetectable are broken. It's a reminder that just because something feels impossible to measure, it doesn't mean the universe has a rule forbidding it; sometimes, it just means we haven't found the right way to ask the question.

Problem
The paper addresses a foundational claim within the philosophy of physics: that absolute velocity is inherently undetectable in a Newtonian universe. While Newton postulated the existence of absolute space and absolute velocity as real, objective features of the world, he and subsequent generations of physicists and philosophers have argued that these properties cannot be empirically observed. The standard view holds that Newtonian dynamics itself guarantees the impossibility of detecting absolute velocity, often citing the Galilean invariance of relative quantities as the formal proof. The authors challenge the validity of this consensus, specifically questioning whether the undetectability of absolute velocity can be derived solely from the formal apparatus of Newtonian mechanics without circular reasoning.

Methodology
The authors employ a conceptual and formal analysis of the Newtonian framework, focusing on the logical structure of arguments used to prove the undetectability of absolute velocity. Their methodology involves:

Deconstructing Standard Arguments: They examine the classic argument that because forces depend only on relative quantities (positions and velocities), and because relative quantities are Galilean invariant, absolute velocities must be undetectable.
Analyzing the Notion of Detection: They define detection broadly as a process where a measuring device ( $M$ ) and a system ( $S$ ) interact such that properties of $S$ become correlated with properties of $M$ . They argue that unless a theory formally restricts which degrees of freedom can encode measurement results, any objective physical property could, in principle, serve as a record.
Critiquing Influential Analyses: The paper scrutinizes specific arguments by Roberts (2008) and Wallace (2022). It identifies that Roberts relies on anthropic assumptions about communication in our actual universe (which is not Newtonian) to prove a theoretical point about a hypothetical Newtonian universe. It argues that Wallace imposes an unjustified stipulation that measurement readouts must be independent of symmetry-variant quantities.
Constructing Counter-Examples: The authors demonstrate that within a Newtonian universe where forces depend only on relative quantities, it is still possible to establish correlations between the absolute velocity of a system and the absolute velocity of a measuring device. They use the example of a one-dimensional elastic collision to show that the final absolute velocity of a detector can encode the initial absolute velocity of a target, even if the interaction itself is purely relational.

Key Contributions

Identification of Circular Reasoning: The primary contribution is the demonstration that standard arguments for the undetectability of absolute velocity are question-begging. The authors show that these arguments implicitly assume the conclusion (that only Galilean-invariant quantities are detectable) rather than deriving it from Newton's laws.
Formal Equivalence of Detection Protocols: The paper establishes that, regarding formal features relevant to detection, absolute and relative velocities behave identically. Both allow for adequate measurement protocols, the establishment of necessary correlations, and the satisfaction of required counterfactuals.
Decoupling of Recording and Detectability: The authors clarify that while the recording of an absolute velocity measurement cannot be done in terms of relative properties (due to the decoupling of the center of mass from relational degrees of freedom), this does not imply the property is undetectable. Detection can occur if the result is recorded in terms of absolute properties (e.g., the final absolute velocity of the detector).
Critique of Anthropocentric Stipulations: The paper argues against importing empirical facts from our actual universe (where absolute velocity appears undetectable) into the theoretical analysis of a hypothetical Newtonian universe.

Results
The analysis yields the following results:

There are no formal reasons within the Newtonian framework to conclude that absolute velocity is undetectable.
The claim that absolute velocity is undetectable relies on an arbitrary stipulation that measurement records must be restricted to relational (Galilean-invariant) quantities.
In a Newtonian universe, a measuring device can successfully measure the absolute velocity of a system by correlating the system's initial absolute velocity with the device's final absolute velocity, even if the interaction forces are purely relational.
The arguments presented by Roberts (2008) and Wallace (2022) fail to provide a non-circular, formal proof of undetectability because they rely on external assumptions or unjustified restrictions on measurement records.

Significance
The paper claims that its significance lies in correcting a fundamental misunderstanding in the philosophy of physics regarding the relationship between formal theory and empirical detectability. The authors argue that the standard view—that Newtonian dynamics itself guarantees the impossibility of detecting absolute velocity—is incorrect. Instead, the undetectability of absolute velocity in our world is an empirical fact, not a necessary consequence of Newtonian formalism.

The broader implication, as stated by the authors, is a methodological lesson for the philosophy of science: one must be suspicious of any claim within a physical theory that posits the existence of "real-but-undetectable" entities. Such claims often rely on arbitrary stipulations about what counts as a detectable record rather than deriving from the theory's formal principles. The authors suggest that this analysis casts doubt on other alleged cases of "in-principle" indiscernibility between physical theories, such as those discussed in the context of de Broglie-Bohm pilot-wave theory, and warns against using empirical adequacy to motivate theoretical restrictions on detectability.

The Great Cosmic Speed Trap

The Paper's Big Twist

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