The concept described in this paper seems so simple that it is astonishing that no one has done it before: map the masses and radii of all categories of objects, from subatomic particles to superclusters of galaxies, onto a global map.
Now that Dr. Charles Lineweaver and graduate student Vihan Patel have finally pulled it off , the results raise some very intriguing and perhaps even troubling questions.
Lineweaver and Patel used a logarithmic plot because nothing else could cover such a wide range of values in both size and mass. Some areas are completely “forbidden” by the known laws of physics, and this is where quantum mechanics comes into play.
“Quantum mechanics blurs the very nature of what it really means to be a single object [referring to fundamental particles],” Patel said.
Perhaps the most significant part of the diagram (below) is the black line separating the area labeled “forbidden by gravity” from the space populated by familiar objects. Black holes are located along this line .
“The more mass a black hole has, the lower its density,” Lineweaver explained.
Although the left side of the line is theoretical, astronomers have observed a range of black hole sizes from the remnants of collapsing stars to the largest supermassive black holes , so this pattern is established and understood.
However, following the line upward, we learn that the entire observable Universe – the region within the Hubble radius (volume) – is also on this line.
In other words, if a black hole were the same size as the Universe we see, then it would have the same density as the Universe. Maybe our Universe is a giant black hole? If the answer is yes, what does that mean?
Lineweaver noted that he and Patel are not the first scientists to wonder whether the entire universe could be a black hole, although others have arrived at the idea in other ways.
The measure of mass chosen by Lineweaver and Patel includes dark matter and dark energy (since energy and mass are interchangeable). As the Universe within the Hubble radius increased in size, so did its total mass/energy due to the increase in dark energy.
Billions of years ago, when the Hubble radius was much smaller, the Universe was also in the line of black holes, so it is unlikely that its position is just a coincidence.
Lineweaver notes that there is an event horizon around the observable Universe (meaning that 94% of the galaxies in the Universe are constantly beyond our reach), just like there is around a black hole, and this is just one of the parallels between them.
However, Lineweaver also emphasized that the Universe being a black hole requires the assumption that everything beyond the Hubble radius is zero-density Minkowski space (roughly speaking, a vacuum). Most cosmologists, including Lineweaver, consider this a bad assumption, leaving the implications of their global map unclear.
“The universe could be an inside-out black hole,” he added.
Overall, the scientist believes that this issue requires much more thought.
The obstacle to answering the question of whether the Universe is a black hole, or at least something related to it, is that we know nothing about the inner workings of black holes. As Stephen Hawking and Roger Penrose noted , general relativity and quantum mechanics give different answers to such questions, and this contradiction has not gone away.
The chart also raises questions about the nature of the universe’s beginnings. “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.”
Instanton is a special type of fluctuation of a quantum field in a vacuum, in which a strong gluon field spontaneously flares up and goes out.
Although the term “singularity” is much more associated in the public consciousness with the Big Bang , Lineweaver said people should become more familiar with the instanton, which he considers a more plausible model for the origin of the universe.
The study is published open access in the American Journal of Physics.