In a new paper, astrophysicists from Australian National University present an overview of the thermal history of our Universe and the sequence of objects (e.g., protons, planets, and galaxies) that condensed out of the background as the Universe expanded and cooled. Their comprehensive pedagogical plots draw attention to the triangular regions forbidden by general relativity and quantum uncertainty, and help navigate the relationship between gravity and quantum mechanics. Their plot of all objects also seems to suggest that the Universe is a black hole.
Masses, sizes, and relative densities of objects in our Universe. Image credit: Charles H. Lineweaver & Vihan M. Patel, doi: 10.1119/5.0150209.
“I set out wanting to understand where all the objects in the Universe came from,” said Australian National University’s Dr. Charley Lineweaver, lead author of the study.
“When the Universe began 13.8 billion years ago in a hot Big Bang, there were no objects like protons, atoms, people, planets, stars or galaxies. Now the Universe is full of such objects.”
“The relatively simple answer to where they came from is that, as the Universe cooled, all of these objects condensed out of a hot background.”
To show this process in the simplest possible way, Dr. Lineweaver and his colleague, Australian National University student Vihan Patel, made two plots.
The first shows temperature and density of the Universe as it expanded and cooled.
The second plots the mass and size of all objects in the Universe.
The result is the most comprehensive chart ever created of all the objects in the Universe.
“The project raised some important questions,” Patel said.
“Parts of this plot are ‘forbidden’ — where objects cannot be denser than black holes, or are so small, quantum mechanics blurs the very nature of what it really means to be a singular object.”
The boundaries of the plots and what lies beyond them are also a major mystery.
“At the smaller end, the place where quantum mechanics and general relativity meet is the smallest possible object — an instanton,” Patel said.
“This plot suggests the Universe may have started as an instanton, which has a specific size and mass, rather than a singularity, which is a hypothetical point of infinite density and temperature.”
“On the larger end, the plot suggests that if there were nothing — a complete vacuum — beyond the observable Universe, our Universe would be a large, low density black hole.”
“This is a little scary, but we have good reason to believe that’s not the case.”
The paper was published in the American Journal of Physics.
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Charles H. Lineweaver & Vihan M. Patel. 2023. All objects and some questions. Am. J. Phys 91 (10): 819-825; doi: 10.1119/5.0150209
