The Illusion of Time

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No Big Bang? Quantum equation predicts universe has no beginning

 via phys.org

The universe may have existed forever, according to a new model that applies quantum correction terms to complement Einstein's theory of general relativity. The model may also account for dark matter and dark energy, resolving multiple problems at once.

The widely accepted age of the universe, as estimated by general relativity, is 13.8 billion years. In the beginning, everything in existence is thought to have occupied a single infinitely dense point, or singularity. Only after this point began to expand in a "Big Bang" did the universe officially begin.

Although the Big Bang singularity arises directly and unavoidably from the mathematics of general relativity, some scientists see it as problematic because the math can explain only what happened immediately after—not at or before—the singularity.

"The Big Bang singularity is the most serious problem of general relativity because the laws of physics appear to break down there," Ahmed Farag Ali at Benha University and the Zewail City of Science and Technology, both in Egypt, told Phys.org.

Ali and coauthor Saurya Das at the University of Lethbridge in Alberta, Canada, have shown in a paper published in Physics Letters B that the Big Bang singularity can be resolved by their new model in which the universe has no beginning and no end.

Old ideas revisited

The physicists emphasize that their quantum correction terms are not applied ad hoc in an attempt to specifically eliminate the Big Bang singularity. Their work is based on ideas by the theoretical physicist David Bohm, who is also known for his contributions to the philosophy of physics. Starting in the 1950s, Bohm explored replacing classical geodesics (the shortest path between two points on a curved surface) with quantum trajectories.

In their paper, Ali and Das applied these Bohmian trajectories to an equation developed in the 1950s by physicist Amal Kumar Raychaudhuri at Presidency University in Kolkata, India. Raychaudhuri was also Das's teacher when he was an undergraduate student of that institution in the '90s.

Using the quantum-corrected Raychaudhuri equation, Ali and Das derived quantum-corrected Friedmann equations, which describe the expansion and evolution of universe (including the Big Bang) within the context of general relativity. Although it's not a true theory of quantum gravity, the model does contain elements from both quantum theory and general relativity. Ali and Das also expect their results to hold even if and when a full theory of quantum gravity is formulated.

No singularities nor dark stuff

In addition to not predicting a Big Bang singularity, the new model does not predict a "big crunch" singularity, either. In general relativity, one possible fate of the universe is that it starts to shrink until it collapses in on itself in a big crunch and becomes an infinitely dense point once again.

Ali and Das explain in their paper that their model avoids singularities because of a key difference between classical geodesics and Bohmian trajectories. Classical geodesics eventually cross each other, and the points at which they converge are singularities. In contrast, Bohmian trajectories never cross each other, so singularities do not appear in the equations.

In cosmological terms, the scientists explain that the quantum corrections can be thought of as a cosmological constant term (without the need for dark energy) and a radiation term. These terms keep the universe at a finite size, and therefore give it an infinite age. The terms also make predictions that agree closely with current observations of the cosmological constant and density of the universe.

New gravity particle

In physical terms, the model describes the universe as being filled with a quantum fluid. The scientists propose that this fluid might be composed of gravitons—hypothetical massless particles that mediate the force of gravity. If they exist, gravitons are thought to play a key role in a theory of quantum gravity.

In a related paper, Das and another collaborator, Rajat Bhaduri of McMaster University, Canada, have lent further credence to this model. They show that gravitons can form a Bose-Einstein condensate (named after Einstein and another Indian physicist, Satyendranath Bose) at temperatures that were present in the universe at all epochs.

Motivated by the model's potential to resolve the Big Bang singularity and account for dark matter and dark energy, the physicists plan to analyze their model more rigorously in the future. Their future work includes redoing their study while taking into account small inhomogeneous and anisotropic perturbations, but they do not expect small perturbations to significantly affect the results.

"It is satisfying to note that such straightforward corrections can potentially resolve so many issues at once," Das said.

The Unreality of Time

Philosophy and physics may seem like polar opposites, but they regularly address quite similar questions. Recently, physicists have revisited a topic with modern philosophical origins dating over a century ago: the unreality of time. What if the passage of time were merely an illusion? Can a world without time make sense?

While a world without the familiar passage of time may seem far-fetched, big names in physics, such as string theory pioneer Ed Witten and theorist Brian Greene, have recently embraced such an idea. A timeless reality may help reconcile differences between quantum mechanics and relativity, but how can we make sense of such a world? If physics does indeed suggest that the flow of time is illusory, then philosophy may be able to shed light on such a strange notion.

British philosopher J.M.E McTaggart advanced this idea in 1908 in his paper titled, “The Unreality of Time.” Philosophers widely consider his paper to be one of the most influential, early examinations of this possibility. Looking through McTaggart’s philosophical lens, a reality without time becomes a little more intuitive and, in principle, possible.

A Tale of Two Times

McTaggart’s argument against the reality of time has a number of interpretations, but his argument starts with a distinction about ordering events in time. The “A” series and “B” series of time form an integral part of McTaggart’s argument, and I’ll unravel this distinction with an example historical event.

On July 20, 1969, Apollo 11 became the first manned spacecraft to land on the moon. For argument’s sake, consider this event to represent an event during the present. Several days in the past (July 16), then, Apollo 11 lifted off the ground. Additionally, several days in the future all of the mission astronauts will land back on earth, safe and sound. Classifying an event as “several days past,” or “several days future,” falls under the “A” series. For the moon landing, some events (e.g. Lincoln’s assassination) are in the distant past; some events are in the distant future (e.g. the inauguration of President Obama); and other events fall somewhere in between.

Under the “A” series, events flow from one classification (i.e. past, present and future) to another. On July 16th, the moon landing would have the property of being in the future. The instant the Apollo 11 landed on the moon, that event would be present. After this moment, its classification changes to the past.

The “B” series, however, doesn’t classify events on this scale ranging from the distant past to the distant future. Instead, the “B” series orders events based on their relationship to other events. Under this ordering, Lincoln’s assassination occurs before the moon landing, and Obama’s inauguration occurs after the moon landing. This relational ordering seems to capture a different way of looking at time.

Two Times, One Contradiction

With this distinction in place, McTaggart additionally argues that a fundamental series of time requires a change to take place. Under the “B” series, the way these events are ordered never change. Obama’s inauguration, for instance, will never change properties and occur before the moon landing and vice versa. These relational properties simply don’t change.

But the A series does embody the change that we might expect from the flow of time. Events first have the property of being in the future, then they become present events. Afterward, they drift into the past. Under the A series, time does have an objective flow, and true change does happen. In McTaggart’s mind (and perhaps the mind of many others), this change is a necessary aspect of time.

But herein lies the contradiction. If these events do change in this sense, they will have contradictory properties. McTaggart argues that an event can’t be in the past, in the present, and in the future. All of these properties are incompatible, so the A series leads to a contradiction. Consequently, time, which requires change, does not truly exist. Welcome to the timeless reality.

Wait a Minute…

Certainly, many philosophers and physicists still believe in the reality of time and have objected to McTaggart’s argument. There are a number of fascinating caveats and counterexamples that you can read about elsewhere. Nonetheless, McTaggart’s work has influenced a number of philosophers’ approach to time, and his work has inspired many philosophers to incorporate physics into their arguments.

For instance, when Albert Einstein introduced special relativity, he seriously disrupted our “folk” conception of the flow of time. In special relativity, there is no absolute simultaneity of events. In one reference frame, two events may appear to happen at the same time. An observer on a speeding rocket ship, however, may observe one event happening before the other. Neither observer is “right” in this situation: This is simply the weirdness that special relativity entails.

Consequently, many philosophers have used special relativity as evidence against a theory supporting the A series of time. If absolute simultaneity doesn’t exist, it doesn’t make sense to say that one event is “in the present.” There’s no absolute present that pervades the universe under special relativity.

But McTaggart’s entire argument may help us better understand strange physics at the intersection of quantum mechanics and general relativity. In an attempt to reconcile these two theories, some well-known physicists have developed theories of quantum gravity that imply the world lacks time in a fundamental way.

Brad Monton, a philosopher of physics at the University of Colorado Boulder, recently published a paper comparing McTaggart’s philosophy with prominent theories in physics, including quantum gravity. During an interview, I asked him how some of the “timeless” ideas in quantum gravity compared to McTaggart.

“They’re on par with the radicalness,” he said. “There’s a lot of radicalness.”

Monton cautioned, however, that quantum gravity does not imply the same lack of time that McTaggart may have had in mind. Physicist John Wheeler, as Monton notes, has postulated that time may not be a fundamental aspect of reality, but this only happens on extremely small distance scales.

Some of these ideas in quantum gravity may be radical, but several respected names in physics are seriously considering a reality without time at its core. If a quantum gravity theory emerges that requires a radical conception of time, McTaggart may help us prepare.

As Monton writes in his paper: “As long as McTaggart’s metaphysics is viable, then the answer to the physicists’ queries is “no” – they are free, from a philosophical perspective at least, to explore theories where time is unreal.”

Many quantum gravity theories remain speculative, but there’s a chance that timelessness may become a prominent feature in physics. If that’s the case, then hopefully philosophers of science will help us wrap our heads around the implications.

From Physics Central