Regain time in space

Physics 15, 75

The development of computer science has the potential to allow cosmic physicists to return the cosmic distribution of matter from today to any point in the history of the universe.

TNG collaboration

Images from computer simulations that model the evolution of matter density and the development of galaxies in the universe.

Today, the universe is a patchwork of galaxies separated by a large band of empty space, but that was not always the case. In the early days before the birth of the galaxy, matter spread more evenly throughout the universe, and blankets covered it to create a newly made bed.

However, the blanket in question had small wrinkles in the form of density fluctuations, like the most carefully placed duvets. Over time, these wrinkles were amplified as gravity attracted more and more material to the slightly denser regions. Researchers can observe the pattern of early wrinkles from what is called the Cosmic Microwave Background (CMB) and see the results by observing today’s universe, but what happened in the meantime? It remains a mystery. Currently, Sebastian von Hausegger and colleagues at Oxford University in the United Kingdom have developed a method for predicting the former material distribution from the later material distribution. [1].. This method has the potential to empower space physicists to rewind the clock at any point in the history of the universe, giving them a better understanding of how the galaxy has evolved.

The transformation of the universe from matter blankets to galaxy patchwork has not been smooth. Initially, wrinkle amplification progressed slowly, the overall pattern remained about the same, and wrinkles became higher (more dense). However, at some point, the denser areas became very dense and suddenly contracted due to gravity. This process blurs the first wrinkle pattern.

Today, it is very difficult to derive the first wrinkle pattern from the location of the galaxy. Instead, astronomers infer it from the CMB. This gives a trace of the material distribution when the universe was about 380,000 years ago. However, the CMB tells only part of the story, so von Hauzeger and his colleagues chose another route to extract the first wrinkle pattern. “By moving the galaxy back into the past, starting today, we can undo the flushes and distortions and reconstruct them accurately. [Universe’s] You can use the initial density field to get a better idea of ​​what it looks like, “says von Hauzeger.

On their method, von Hauseger and his colleagues turned to an idea from mathematics called optimal transportation theory. This theory is used to calculate the most efficient way to move things from one place to another. Originally devised in the 18th century for optimal excavation and removal of soil from construction sites, the theory has since been applied to problems ranging from image restoration to the discovery of hidden patterns in human tissue. (See Viewpoint: Excavating the Topology to Find the Structure). Large-scale calculations using theory are known to take time, but recent advances in computer science, especially shortcuts devised by one of von Hausegger’s colleagues, make the best transportation theory far beyond the computer. Can now be implemented efficiently.

In their demonstration, the team used a computer simulation of the universe to reproduce the time evolution of large-scale features in matter distribution. From that simulation, they chose a late-time snapshot of today’s universe. We then incorporated the simulated snapshot into the algorithm and ran it in the opposite direction to predict what the simulated universe would look like in the early days. The team then compared the predicted initial material distribution with an initial snapshot from the simulation. “We’re basically playing games that pretend we didn’t know what things looked like in the early days,” says von Hauzeger.

To make their comparison, the team extracted a set of subtle but well-defined densities called baryon acoustic oscillations (BAOs) from predicted and simulated snapshots. These wiggle length prominent scales can be calculated from cosmological models (see Overview: More Directly Measured Space Rulers) and are a “good benchmark” for testing, von Hauseger said. increase. The same value was found with high accuracy in both images. This shows that their method worked.

The reconstruction of BAO functionality is done with “unprecedented accuracy,” says Ravi Sheth, an astrophysicist at the University of Pennsylvania. Sheth is currently working with two other researchers in the study, Bruno Lévy of the University of Lorraine and Roya Mohayee of the Institute of Astronomical Physics in Paris, to take the next step in this method. Sheth says the good thing about this task is that it uses simple assumptions that everyone agrees on.

The team is now adapting the code behind the method so that it works in the actual universe instead of the simulated universe. “Of course, the idea is to use real data. This is definitely the next step,” says von Hauzeger.

– Katharine Wright

Katharine Wright is Deputy Editor-in-Chief Physics..


  1. S. von Hauze Gar et al.“Reconstruction of accurate baryon acoustic oscillations by semi-discrete optimal transport” Pastor Physics Let 128201302 (2022).

Subject area

Recent articles

Neutrinos from black hole snacks
Ionized black hole
Rethinking the cosmological conundrum

Other articles

Leave a Comment