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CROCS Data Release I: Constraints on the Hubble Constant

This satirical paper humorously claims to resolve the Hubble tension by attributing the discrepancy between Planck and SH0ES measurements to "imperial biasing systematics" and proposing that converting units to the metric system reconciles the data to a value of $H_0 = 69.00\pm0.420$ km $\text{s}^{-1}\text{Mpc}^{-1}$ .

Original authors: Luke Weisenbach, Sophie L. Newman, Kieran Graham, Sai S. Dhavala, Benjamin Floyd, Neel Shah, Gemini 3 Flash, The CROCS Collaboration

Published 2026-04-01

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CC BY 4.0

Original authors: Luke Weisenbach, Sophie L. Newman, Kieran Graham, Sai S. Dhavala, Benjamin Floyd, Neel Shah, Gemini 3 Flash, The CROCS Collaboration

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 Shoe-Box Cosmology Prank: A Simple Explanation

Imagine the scientific community as a group of very serious detectives trying to solve a mystery: How fast is the universe expanding?

For years, two top detective teams have been arguing.

Team A (Planck) looked at the "baby photos" of the universe (the Cosmic Microwave Background) and calculated the speed is 67.
Team B (SH0ES) looked at the "adult photos" (distant exploding stars) and calculated the speed is 73.

The numbers don't match. The difference is so big that it's like two people measuring the same table and one getting "3 feet" and the other getting "4 feet." This disagreement is called the "Hubble Tension," and it has been keeping physicists up at night for a decade.

Enter the CROCS Collaboration. They are a group of scientists (and a few people who definitely shouldn't be there, like an astrologer and a Google AI) who decided to solve this mystery with a very specific, very silly approach.

Here is what their paper claims, translated into plain English:

1. The "Magic" Roundabout Theory

The authors suggest that the universe isn't expanding weirdly; instead, traffic in Swindon, England, is messing up the data.

They point to the "Swindon Magic Roundabout," a famous, confusing intersection with five mini-roundabouts inside one big one. They jokingly claim that light from distant stars gets "stuck" in the loops of this roundabout, just like a car. Because the light takes longer to get through the traffic, the stars look further away than they really are. This fake distance makes the universe look like it's expanding faster than it actually is.

The Metaphor: Imagine you are trying to time how fast a runner is going. But every time they run past a confusing maze in the middle of the track, they get stuck for a few seconds. You think they are slow, but actually, the maze is just wasting their time.

2. The "Croc" Connection

The paper's name, CROCS, stands for "Cosmologists Researching On Cosmological Scales," but the authors are also obsessed with Croc shoes.

They argue that the 13 holes on the top of a Croc shoe are a secret code. They claim these 13 holes represent the 13.8 billion-year age of the universe. They even suggest that when you put a Croc in "Sport Mode" (strapping the heel back), it changes the curvature of space-time around your ankle, which somehow fixes the math for the whole universe.

The Metaphor: It's like saying the reason the stock market is crashing is because the CEO's shoes have a specific number of holes in them.

3. The "Imperial" Mistake (The Punchline)

After all the jokes about traffic and shoes, they drop the "real" solution. They claim the Hubble Tension exists because of a unit conversion error.

They argue that the scientists measuring the universe are secretly doing their math in Imperial units (miles and inches) but reporting the results in Metric units (kilometers and meters).

They say Team A (Europe) and Team B (USA) are both guilty of this "Imperial Biasing Systematic."
They claim that if you just convert everything properly, the two different numbers (67 and 73) magically become the exact same number: 69.
The Metaphor: It's like two people arguing about the price of a car. One says it costs $100, and the other says it costs £100. They are fighting over a huge difference until someone realizes, "Oh, you're both using different currencies! If we convert them, they are actually the same price."

4. The "Secret" Data

The paper includes a massive list of "CROCS objects" (stars and galaxies) with coordinates and data. However, if you look closely, the data is nonsense. Some of the "observations" were made in 3 days and 27 minutes, but the authors claim this is actually 61 days because the lead author was traveling at near the speed of light (a joke about Einstein's relativity).

They also admit they didn't actually do any real work. The "Fisher Matrix" (a complex math tool used to prove their results) is just a picture of a shoe with a zero in it.

The Big Reveal

This paper is an April Fools' Joke.

It was submitted on April 1, 2026 (a future date in the text) to the Monthly Notices of the Royal Astrological Society (a fake journal name, mixing "Astronomical" with "Astrological").

The Real Message:
The authors are poking fun at how desperate scientists are to solve the Hubble Tension. They are saying, "We've tried so many crazy theories (dark energy, new physics, local voids) that we might as well blame it on traffic jams, shoe holes, or unit conversion errors."

It's a reminder that in science, sometimes the answer isn't a new particle or a new law of physics—it might just be a simple mistake, or in this case, a very good joke.

In short: The universe isn't broken. The paper is just a very clever, very long, very mathematical prank to make us laugh at how complicated cosmology has become.

Important Note: The document provided is a satirical April Fools' paper submitted to Monthly Notices of the Royal Astronomical Society (MNRAS) on April 1, 2026. It is written in the style of a rigorous academic paper but contains absurd premises, fake data, and nonsensical conclusions intended to parody cosmological research and the "Hubble Tension."

Below is a technical summary of the paper's content, treating the text as a self-contained document while acknowledging its satirical nature.

Paper Title: CROCS Data Release I: Constraints on the Hubble Constant

Authors: Luke Weisenbach et al. (The CROCS Collaboration)
Date: April 1, 2026 (Draft)

1. Problem Statement

The paper addresses the Hubble Tension, a persistent $5.5\sigma$ discrepancy between two independent measurements of the Hubble constant ( $H_0$ ):

Early Universe (Planck): $67.27 \pm 0.60 \, \text{km s}^{-1} \text{Mpc}^{-1}$ (derived from CMB anisotropies).
Late Universe (SH0ES): $73.2 \pm 1.3 \, \text{km s}^{-1} \text{Mpc}^{-1}$ (derived from Type Ia supernovae and Cepheid variables).

The authors note that decades of proposed "new physics" solutions (e.g., early dark energy, modified gravity) have failed to resolve this tension. They propose that the discrepancy may not be due to new physics, but rather a fundamental, "embarrassingly straightforward" systematic error common to both teams.

2. Methodology

The CROCS (Cosmologists Researching On Cosmological Scales) collaboration employs a multi-faceted, albeit satirical, approach:

Data Collection: The authors claim to have gathered a proprietary dataset (DR1) consisting of $\sim3$ days and 27 minutes of observation time. The data is described as "commercially sensitive" and largely under embargo, preventing independent verification.
Fisher Matrix Analysis: A formal Fisher information matrix analysis is performed on parameters $\theta = (H_0, \sigma_8)$ . The resulting matrix yields a projected $1\sigma$ uncertainty of $\Delta H_0 = 0.420 \, \text{km s}^{-1} \text{Mpc}^{-1}$ and a zero eigenvalue for $\sigma_8$ , which the authors use to dismiss the $\sigma_8$ tension as non-existent.
Systematic Identification (The "IBS"): The core methodology involves identifying a new systematic error termed the Imperial Biasing Systematic (IBS). The authors hypothesize that both the Planck (European) and SH0ES (US) collaborations inadvertently conducted internal analyses using Imperial units (miles) rather than SI units (kilometers), despite reporting results in metric.
Corrections:
- Swindon Roundabout Effect: The paper posits that the "Swindon Magic Roundabout" in the UK acts as a gravitational lens or photon trap, introducing time delays that bias distance ladder measurements.
- Unit Conversion: The primary correction involves applying a conversion factor ( $f_{IBS} \approx 1.60934$ ) to convert the "imperial" internal values back to metric, effectively reconciling the two datasets.
AI Collaboration: Section 4 is explicitly noted as being written by "Gemini 3 Flash," introducing the "Foam-O-Static Inflation Theory," which links the 13 ventilation holes on a Croc shoe to the age of the universe (13.8 billion years).

3. Key Contributions

Definition of "Magic" Roundabouts: The paper provides the first peer-reviewed definition of a "Magic Roundabout" based on navigational confusion ( $>3\sigma$ ) and heritage status, specifically validating the Swindon roundabout while stripping the "magic" designation from the Hemel Hempstead roundabout.
The Imperial Biasing Systematic (IBS): The introduction of IBS as a novel systematic error source, arguing that unit confusion between Imperial and Metric systems is the root cause of the Hubble Tension.
Dismissal of $\sigma_8$ Tension: A formal (though logically flawed) proof in the Appendix arguing that the $\sigma_8$ tension does not exist because it is "not interesting" and "no crocs are involved."
CROCS Catalog: The release of a catalog (Table 2) of "CROCS objects" (C1813, C1275, etc.) with coordinates (RA, Dec), redshift ( $z$ ), and magnitude, presented as astronomical data but clearly fabricated for the satire.

4. Results

Resolution of Hubble Tension: By applying the IBS correction factor ( $f_{IBS}^{-1}$ ) and a calibration constant $C$ (chosen arbitrarily to ensure dimensional consistency), the authors claim to reconcile both measurements:
$H_{Planck, corr}^0 = 69.00 \, \text{km s}^{-1} \text{Mpc}^{-1}$
$H_{SH0ES, corr}^0 = 69.00 \, \text{km s}^{-1} \text{Mpc}^{-1}$
Final Value: The paper reports a new, definitive value for the Hubble constant:
$H_0 = 69.00 \pm 0.420 \, \text{km s}^{-1} \text{Mpc}^{-1}$
Relativistic Time Dilation: The authors explain the discrepancy between the 61-day calendar duration of the project and the reported "3 days and 27 minutes" of observing time by claiming the lead author was traveling at $v \approx 0.9997c$ relative to the rest of the collaboration, invoking Lorentz time dilation.

5. Significance and Conclusion

Scientific Impact (Satirical): The paper claims to have "resolved the Hubble tension for good" without requiring new particles, fields, or interactions. It suggests the entire field of cosmology has been misled by a simple unit conversion error.
Cultural Commentary: The paper satirizes the desperation of the cosmological community to find "new physics" to solve the tension, suggesting instead that the solution is mundane (unit conversion) or absurd (shoe holes). It also mocks the inclusion of non-scientific fields (astrology) and the "black box" nature of proprietary data in modern science.
Conclusion: The authors declare the Hubble tension an "artefact of IBS" and expect the field to "move on promptly." The paper concludes with acknowledgments to the "anonymous referee" for not reading the manuscript and thanks to various pop culture figures and locations.

Summary: This paper is a sophisticated parody of high-energy astrophysics literature. It mimics the structure, tone, and mathematical formalism of a real research article (including Fisher matrices, LaTeX formatting, and extensive tables) to deliver a humorous critique of scientific rigor, the pressure to publish, and the complexity of the Hubble Tension. The "results" are mathematically consistent within the paper's internal logic but physically nonsensical.