This simulation demonstrates one of the most important claims in the Big Flare-Up Theory: the apparent accelerating expansion of the universe — the discovery that won the Nobel Prize and led to the invention of "dark energy" — is not real. It is an illusion created by our own motion through space.
We are not stationary observers. Our entire local group of galaxies is moving at roughly 550–627 km/s relative to the background of the universe. When a moving observer measures recession velocities, galaxies in the direction of travel appear to recede slower, and galaxies behind appear to recede faster. This creates a directional asymmetry — called a dipole — that looks exactly like accelerating expansion. But it is nothing more than observer motion.
1,000 galaxies are distributed across a region of space. Their recession velocities are calculated using the standard Hubble formula — velocity proportional to distance. There is no dark energy anywhere in this simulation. There is no accelerating expansion. Space is not stretching.
The only thing added is what we know to be physically true: our observer is moving. The simulation then asks — if we are moving at 550 km/s in a specific direction, what does the universe look like from our perspective? The answer appears in four live plots.
You can drag the Bulk Flow slider to zero at any time and watch the entire dark energy signal disappear. Every asymmetry, every directional H₀ difference, every dipole wave — all of it vanishes the moment the observer stops moving. Set it back to 550 and it all returns. This is the dark energy illusion.
The key question this simulation answers: If someone in a moving car measures the speed of passing cars, do they get the true speed of those cars? No — they get the speed relative to their own motion. Scale that up to the entire universe. An observer moving at 550 km/s through space will measure systematically higher recession velocities in one direction and lower in the other. That directional difference is exactly what Colin et al. found in real supernova data in 2019, at 3.9 sigma statistical significance.
In 2019, a team of researchers reanalysed 740 Type Ia supernovae from the Joint Light-curve Analysis catalogue — the same dataset that won the Nobel Prize for discovering dark energy. They found the apparent acceleration is not the same in all directions. It is stronger in one direction and weaker in the opposite direction. The asymmetry aligns with the CMB dipole — the known direction of our motion through space.
Their conclusion was direct: "the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of dark energy in the Universe." This paper was published in a peer-reviewed journal in 2019 and has not been refuted.
What this means for the standard model: Dark energy is supposed to comprise 68% of everything in the universe. It has never been directly detected — not once, in any experiment. The entire case for its existence rests on the supernova acceleration signal. If that signal is an artefact of our own motion, then the evidence for 68% of the universe's proposed content disappears. BFUT predicted this mechanism independently.
What this means for BFUT: In an infinite universe with no expansion, our local bulk motion naturally produces the observed asymmetry. No new physics is required. No undetected substance is required. The Hubble Law is preserved perfectly. The universe is not accelerating. We are moving — and that motion creates the illusion of acceleration in one half of the sky.
Every number updates live as you change the sliders. Here is exactly what each one is telling you.
This is the Hubble constant recovered from all 1,000 galaxies by fitting a straight line through the Hubble Diagram. It should be very close to the H₀ Input slider — if you set 70, it will recover approximately 70.0.
This confirms a critical BFUT point: the Hubble Law is reproduced perfectly without any expansion of space. Bulk motion does not destroy it — it only distorts the measurement directionally.
These are Hubble constants fitted separately for galaxies in our direction of travel (red) versus galaxies in the opposite direction (blue). They will be different — even though the same H₀ generated all the velocities.
An astronomer who only surveys half the sky will measure a different expansion rate than one surveying the other half. Neither is wrong. The universe genuinely looks different in each direction — because we are moving. This is the Hubble Tension.
This measures how statistically significant the directional asymmetry is, in sigma (σ). In physics, 3σ is considered a strong detection. 5σ is considered a definitive discovery.
Colin et al. (2019) found 3.9σ in 740 real supernovae. At default settings this simulation produces a similar sigma value from pure bulk motion — with no dark energy and no expansion in the physics. At 200 Mpc max distance the signal rises further, as it does in the real nearby supernova sample.
This is the raw gap in km/s/Mpc between H₀ measured towards our motion versus away. The real Hubble Tension between Planck (67–68 km/s/Mpc) and local distance ladder measurements (73–74 km/s/Mpc) is approximately 6 km/s/Mpc.
This simulation produces a gap of similar magnitude from pure observer motion at 550 km/s. The Hubble Tension may not require new physics — it may require only the acknowledgement that we are not a stationary observer.
Each dot is one of the 1,000 simulated galaxies. Position left-to-right shows distance from us (Mpc). Position bottom-to-top shows how fast it appears to be moving away (km/s). The colour shows its redshift — how much its light is stretched. Blue means lower redshift. Yellow and red mean higher redshift.
The red dashed line is the best-fit Hubble Law. It is straight and tight. This is the same Hubble pattern that Big Bang cosmologists cite as evidence for universal expansion — reproduced here with zero expansion in the physics. The fitted H₀ value printed on the chart closely matches the slider setting. The Hubble Law is confirmed. Expansion is not the only mechanism that produces it.
This splits the 1,000 galaxies by direction. Red dots are galaxies within 60° of where we are heading. These are the galaxies we are moving toward — our motion partially cancels their recession, so they appear to recede more slowly. Blue dots are galaxies behind us — our motion adds to their recession, so they appear to recede faster.
The red trend line is steeper than the blue trend line. Steeper means higher measured H₀. This means: if an astronomer only surveys galaxies behind us, they measure higher expansion than an astronomer who only surveys galaxies ahead. Both are measuring the same universe. The difference is pure observer motion.
This is precisely the pattern Colin et al. found in 740 real supernovae in 2019, at 3.9 sigma significance. The H₀ values shown on this chart — one red, one blue — mirror the real-world tension between the Planck H₀ measurement and the local distance ladder H₀ measurement.
This is the full sky seen from our observer, projected flat like a world map. The green vertical line marks the direction of our bulk motion. Each dot is a galaxy. Size indicates distance — larger dots are farther away. Colour indicates redshift.
Warm colours (yellow, orange, red) on the right side of the map: these are galaxies we are moving away from. Their recession looks faster because our motion adds to it. Cool colours (blue, cyan) on the left: these are galaxies we are moving toward. Their recession looks slower because our motion partially cancels it. The two halves of the sky look different — not because the universe is different in different directions, but because we are moving through it.
When you set Bulk Flow to zero, this map becomes a uniform colour. The asymmetry disappears completely. It was never a property of the universe. It was always a property of the observer.
After fitting the Hubble Law to all galaxies, this plot shows how much each galaxy's velocity deviates from that average fit — its residual. If the universe were perfectly isotropic (identical in all directions), these residuals would scatter randomly with no pattern at all.
Instead, you see a clear wave. Galaxies at 0° — directly ahead of our motion — have positive residuals: they appear faster than the Hubble fit predicts. Galaxies at 180° — directly behind us — have negative residuals: they appear slower. The orange line traces the average residual in each direction band, making the wave visible.
This sinusoidal wave is called a dipole. Its amplitude, measured in sigma, is the Dipole Signal number in the stats bar. Colin et al. found this exact wave pattern in real supernovae in 2019. This simulation reproduces it from first principles — pure observer motion, no dark energy required.
This simulation has been independently verified in Python using NumPy and SciPy with identical physics. At default settings (N=1000, H₀=70, bulk flow=550 km/s, max distance=600 Mpc):
This simulation does not prove that dark energy does not exist. It demonstrates that the primary observational evidence for dark energy — the directional asymmetry in Type Ia supernova data — is entirely consistent with, and reproduced by, local bulk observer motion alone.
The simulation uses simplified physics: point particles, uniform H₀, and a single bulk flow vector. Real cosmological data involves peculiar velocities, light-curve fitting, measurement uncertainties, and complex selection effects. The signal this simulation produces is qualitatively identical to the Colin et al. finding but is not a numerical reproduction of it.
The scientific status of Colin et al. (2019): Published in Astronomy & Astrophysics, a leading peer-reviewed journal. Reanalysis of the full JLA supernova catalogue of 740 objects. Finding: the deceleration parameter exhibits a 3.9σ dipole aligned with the CMB dipole direction. Conclusion: cosmic acceleration may be an artefact of observer motion. The paper has not been refuted. The Nobel Prize for dark energy was awarded on the assumption of isotropy. Colin et al. showed that assumption does not hold in the data.
BFUT does not deny any observation. It challenges the interpretation. The Hubble recession is real. The CMB is real. The supernova redshifts are real. What BFUT challenges is the inference from those observations to a singular origin, a stretching fabric of space, and an undetected substance comprising 68% of everything. This simulation provides one concrete demonstration of how a standard observation — the apparent acceleration — can be fully explained without dark energy.