For 100 years since it was published, Einstein’s General Theory of Relativity has mostly passed every kind of test thrown at it. ‘Mostly’ is a keyword here. Because it implies that there are a few scenarios where the theory doesn’t hold up. And one such case is the existence of singularities.
A singularity is defined as a point where the force of gravity is too overwhelming that the laws of physics break down. General relativity says that an example of such singularity exists at the center of a black hole. It also predicts that a black hole is surrounded by what is referred to as an ‘event horizon’ — a.k.a. the ‘point of no return’ because anything that passes through it gets devoured by the black hole, and nothing (not even light) can escape from gravity’s super-strong pull.
This necessarily implies that it is virtually impossible to observe a black hole and its event horizon from the outside or anywhere near it because whatever is being used will just get sucked in, right? There’s actually a term for this — cosmic censorship conjecture. It simply means that a singularity will always be cloaked from view. This also suggests that outside a black hole, the singularity within will not have any effect, and general relativity’s predictions will remain intact. In short, a singularity can’t possibly form outside a black hole.
Still, there’s a name given — should they happen to be real — to a singularity that exists outside a black hole: naked singularity. Predictions about the existence of such have been done before, but they are typically based on a five-dimensional universe. Which is like saying that it’s impossible for a naked singularity to exist, at least in the universe we know.
So does that mean general relativity will remain uncontested? Maybe. Maybe not. Because according to research recently published in the journal Physical Review Letters, it’s not just possible for a naked singularity to exist in an extraordinary (or maybe fictional?) universe; it can exist in a real universe like ours too.
Based on simulations done by physicists Toby Crisford and Jorge Santos from the University of Cambridge, a four-dimensional universe (three spatial dimensions plus time as the fourth dimension just like ours) can host a naked singularity. If it happens to be saddle-shaped that is.
General relativity does allow for universes of different shapes. And a saddle-shaped one, also called Anti-de Sitter space, is one of those possible shapes.
One of the distinguishing features of a saddle-shaped universe is a point of no return where light doesn’t get trapped, but instead gets reflected back. As described by Crisford to Phys.org: “It’s a bit like having a spacetime in a box. At the boundary, the walls of the box, we have the freedom to specify what the various fields are doing, and we use this freedom to add energy to the system and eventually force the formation of a singularity.”
On the other hand, co-author Santos also says that introducing charged particles in their simulation would probably diminish the formation of the naked singularity. “If true, it could imply a connection between the cosmic censorship conjecture and the weak gravity conjecture, which says that any consistent theory of quantum gravity must contain sufficiently charged particles. In Anti-de Sitter space, the cosmic censorship conjecture might be saved by the weak gravity conjecture,” he explains.
It’s not going to be easy to prove the existence of such an extremely curved saddle-shaped universe, though. Nonetheless, just being possible, is already enough to disrupt what we think we know. And that gives scientists so much more to ponder on, which could hopefully lead to more explanations eventually, instead of more questions.
Disclaimer: This page contains affiliate links. If you choose to make a purchase after clicking a link, we may receive a commission at no additional cost to you. Thank you for your support!
We live in a de Sitter universe, not an anti-de Sitter universe. Why some theoretical physicists chose to ignore this observational fact is beyond me.
Actually Einstein’s relativity theory has already been disproved both logically and experimentally (see “Challenge to the special theory of relativity”, March 1, 2016 on Physics Essays and a press release “Special Theory of Relativity Has Been Disproved Theoretically” on Eurekalert.
The most obvious and indisputable experimental evidence, which everybody with basic knowledge of special relativity should immediately understand: is the existence of the absolute time shown by the universally synchronized clocks on the GPS satellites which move at high velocities relative to each other while special relativity claims that time is relative (i.e. the time on each reference frame is different) and can never be synchronized on clocks moving with relative velocities.
Many physicists claim that clocks on the GPS satellites are corrected according to both special relativity and general relativity. This is not true. The corrections of the atomic clocks on the GPS satellites are nothing to do with relativistic effects because the corrections are absolute changes of the clocks, none of which is relative as claimed by special relativity. After all corrections, the clocks are synchronized not only relative to the ground clocks but also relative to each other.
Some people may argue that the clocks are only synchronized in the earth centered inertial reference frame, and are not synchronized in the reference frames of the GPS satellites. If it were true, then the time difference between a clock on a GPS satellite and a clock on the ground observed in the satellite reference frame would grow while the same clocks observed on the earth centered reference frame were keeping synchronized. If you corrected the clock on the satellite when the difference became significant, the correction would break the synchronization of the clocks observed in the earth centered frame. That is, there is no way to make a correction without breaking the synchronization of the clocks observed in the earth centered frame. Therefore, it is wrong to think that the clocks are not synchronized in the satellite frame. Actually, on the paper mentioned above, I have proved that if clocks are synchronized in one inertial reference frame, then they are synchronized in all inertial reference frames because clock time is absolute and universal.
Similarly, all the differences of the clocks in Hefele-Keating experiment were also absolute (i.e., they were the same no matter whether you observe them on the moon or on the space station). Therefore, they are nothing to do with relative velocity caused time dilation as claimed by special relativity. It is simply a wrong interpretation that the differences of the displayed times of the clocks are the results of relativity.
The increase of the life of a muon in a circular accelerator or going through the atmosphere is also an absolute change which is the same observed in all reference frames.
The simplest thought experiment to disprove special relativity is the symmetric twin paradox: two twins made separate space travels in the same velocity and acceleration relative to the earth all the time during their entire trips but in opposite directions. According to special relativity, each twin should find the other twin’s clock ticking more slowly than his own clock during the entire trip because of the relative velocity between them as we know that acceleration did not have any effect on kinematic time dilation in special relativity. But when they came back to the earth, they found their clocks had exact the same time because of symmetry. This is a contradiction that has disproved special relativity. This thought experiment demonstrates that relativistic time is not our physical time and can never be materialized on physical clocks.
That is, time is absolute and space is 3D Euclidean. There is nothing called spacetime continuum in nature.
I don’t think the GPS satellites move fast enough to have much effect on the positions they calculate based on the time pulse. There are other factors in the orbit that introduce enough error that the time differences due to relativity are within the margin of other errors.
The relativistic time dilation is significant to the accuracy of the cesium atomic clocks and can be easily detected. But the reality is that all the corrections are absolute and the final clocks are synchronized relative to all reference frames which disproves special relativity which claims time is relative and clocks with relative velocities can never be synchronized in multiple reference frames.
But in 4 D space it may be relative as we are 3 D then any 4 D thing is moving for all of us hence then the time will relative so it depends on the absolute dimension in which we are living.
What happens to time near or ‘inside’ of a singularity?
PBS Space time has a great video series on this question:
https://www.youtube.com/watch?v=mht-1c4wc0Q
Fascinating article.Since Einsteins’ theory is just that – ie. a theory which has been a pretty good one for the past 100 years. But,it has now has supposedly has been disproven “theoretically”. How will we ever know for sure since it is all based on theory & conjecture?The very limited knowledge we have based on theory & on the nature of unobservable “black holes” & on the unobservable postulations on “naked singularity” is now being “proved” by scientific simulations which ironically are themselves based on new theory. This now allowsfor an Anti de-sitter space concept which implies that the universe could indeed be shaped like a “saddle” & not a great “cosmic egg” in shape, as previously supposed, in order to fit with these new theoretical postulations. The more we contemplate the wonders of the cosmos, the more humble we humans’ should become, at our limited knowledge of the nature of the universe & at the amazing hand of God, the omniscient Creator of this universe.I wonder what our limited knowledge or theories will look like 100 years from now? Stay tuned!
Okay, humor me on this, please. I have wondered for years if a spherical two way mirror could be created such that light could get in but not out. Sound SOMETHING like a black hole, only different? I just wonder what would result over time, assuming such a thing could be manufactured.
What if black holes are compact stars larger than 1.1 Schwarzschild radius? That would mean there is no such thing as a singularity in nature.