Let's face it: to think that the universe has a history that started with a kind of birthday some 13.8 billion years ago is weird. It resonates with many religious narratives that posit that the cosmos was created by divine intervention, although science has nothing to say about that.
What happened before time began?
If everything that happens can be attributed to a cause, what caused the universe? To deal with the very tough question of the First Cause, religious creation myths use what cultural anthropologists sometimes call a "Positive Being," a supernatural entity. Since time itself had a beginning at some point in the distant past, that First Cause had to be special: it had to be an uncaused cause, a cause that just happened, with nothing preceding it.
Attributing the beginning of everything to the Big Bang begs the question, "What happened before that?" That's a different question when we are dealing with eternal gods, as for them, timelessness is not an issue. They exist outside of time, but we don't. For us, there is no "before" time. Thus, if you ask what was going on before the Big Bang, the question is somewhat meaningless, even if we need it to make sense. Stephen Hawking once equated it with asking, "What's north of the North Pole?" Or, the way I like to phrase it, "Who were you before you were born?"
To ask from science to "explain" the First Cause is to ask science to explain its own structure. It's to ask for a scientific model that uses no precedents, no previous concepts to operate. And science can't do this, just as you can't think without a brain.
Saint Augustine posited that time and space emerged with creation. For him, it was an act of God, of course. But for science?
Scientifically, we try to figure out the way the universe was in its adolescence and infancy by going backward in time, trying to reconstruct what was happening. Somewhat like paleontologists, we identify "fossils" — material remnants of long-ago days — and use them to learn about the different physics that was prevalent then.
The premise is that we are confident that the universe is expanding now and has been for billions of years. "Expansion" here means that the distances between galaxies are increasing; galaxies are receding from one another at a rate that depends on what was inside the universe at different eras, that is, the kinds of stuff that fill up space.
The "Big Bang" was not an explosion
When we mention the Big Bang and expansion, it's hard not to think about an explosion that started everything. Especially since we call it the "Big Bang." But that's the wrong way to think about it. Galaxies move away from one another because they are literally carried by the stretch of space itself. Like an elastic fabric, space stretches out and the galaxies are carried along, like corks floating down a river. So, galaxies are not like pieces of shrapnel flying away from a central explosion. There is no central explosion. The universe expands in all directions and is perfectly democratic: every point is equally important. Someone in a faraway galaxy would see other galaxies moving away just like we do.
(Side note: For galaxies that are close enough to us, there are deviations from this cosmic flow, what's called "local motion." This is due to gravity, The Andromeda galaxy is moving toward us, for example.)
Going back in time
Credit: Andrea Danti / 98473600 via Adobe Stock
Playing the cosmic movie backward, we see matter getting squeezed more and more into a shrinking volume of space. Temperature rises, pressure rises, things break apart. Molecules get broken down into atoms, atoms into nuclei and electrons, atomic nuclei into protons and neutrons, and then protons and neutrons into their constituent quarks. This progressive dismantling of matter into its most basic constituents happens as the clock ticks backward toward the "bang" itself.
For example, hydrogen atoms dissociate at about 400,000 years after the Big Bang, atomic nuclei at about one minute, and protons and neutrons at about one-hundredth of a second. How do we know? We have found the radiation left over from when the first atoms formed (the cosmic microwave background radiation) and discovered how the first light atomic nuclei were made when the universe was merely a few minutes old. These are the cosmic fossils that show us the way backward.
Currently, our experiments can simulate conditions that happened when the universe was roughly one trillionth of a second old. That seems like a ridiculously small number for us, but for a photon — a particle of light — it's a long time, allowing it to travel the diameter of a proton a trillion times. When talking about the early universe, we must let go of our human standards and intuitions of time.
We want to keep going back as close to t = 0 as possible, of course. But eventually we hit a wall of ignorance, and all we can do is extrapolate our current theories, hoping that they will give us some hints of what was going on much earlier, at energies and temperatures we cannot test in the lab. One thing we do know for certain, that really close to t = 0, our current theory describing the properties of space and time, Einstein's general theory of relativity, breaks down.
This is the realm of quantum mechanics, where distances are so tiny that we must rethink space not as a continuous sheet but as a granular environment. Unfortunately, we don't have a good theory to describe this granularity of space or the physics of gravity at the quantum scale (known as quantum gravity). There are candidates, of course, like superstring theory and loop quantum gravity. But currently there is no evidence pointing toward either of the two as a viable description of physics.
Physics' greatest mystery: Michio Kaku explains the God Equation | Big Think www.youtube.com
Quantum cosmology doesn't answer the question
Still, our curiosity insists on pushing the boundaries toward t = 0. What can we say? In the 1980s, James Hartle and Stephen Hawking, Alex Vilenkin, and Andrei Linde separately came up with three models of quantum cosmology, where the whole universe is treated like an atom, with an equation similar to the one used in quantum mechanics. In this equation, the universe would be a wave of probability that essentially links a quantum realm with no time to a classical one with time — i.e., the universe we inhabit, now expanding. The transition from quantum to classical would be the literal emergence of the cosmos, what we call the Big Bang being an uncaused quantum fluctuation as random as radioactive decay: from no time to time.
If we assume that one of these simple models is correct, would that be the scientific explanation for the First Cause? Could we just do away with the need for a cause altogether using the probabilities of quantum physics?
Unfortunately, not. Sure, such a model would be an amazing intellectual feat. It would constitute a tremendous advance in understanding the origin of all things. But it's not good enough. Science can't happen in a vacuum. It needs a conceptual framework to operate, things like space, time, matter, energy, calculus, and conservation laws of quantities like energy and momentum. One can't build a skyscraper out of ideas, and one can't build models without concepts and laws. To ask from science to "explain" the First Cause is to ask science to explain its own structure. It's to ask for a scientific model that uses no precedents, no previous concepts to operate. And science can't do this, just as you can't think without a brain.
The mystery of the First Cause remains. You can choose religious faith as an answer, or you can choose to believe science will conquer it all. But you can also, like the Greek Skeptic Pyrrho, embrace the limits of our reach into the unknowable with humility, celebrating what we have accomplished and will surely keep on accomplishing, without the need to know all and understand all. It's okay to be left wondering.
Curiosity without mystery is blind, and mystery without curiosity is lame.
Astronomers have calculated the first 100 million years of the history of the gigantic Oort cloud – a theoretical entity that contains 100 billion or so comet-like objects and forms a giant spherical shell around the sun and the rest of the solar system. NASA describes it as "a big, thick-walled bubble made of icy pieces of space debris the sizes of mountains and sometimes larger."
The Oort cloud was named after Dutch astronomer Jan Hendrik Oort, who discovered it in the 1950s. He was looking to understand why some comets in the solar system have elongated orbits. Scientists now believe the Oort Cloud is the source of most such comets.
The cloud is believed to be extremely far from the sun, many times more distant than the outer reaches of the Kuiper belt, the area of the solar system past the orbit of Neptune that contains comets, asteroids, and small icy space bodies as well as the dwarf planet Pluto.
According to NASA, the inner edge of the Oort cloud is likely between 2,000 and 5,000 AU (astronomical units or Earth-Sun distances) from the sun. The outer edge is probably 10,000 to 100,000 AU from the sun. By comparison, the Kuiper belt is about 30 to 50 AU away from the sun.
Oort cloud: the leftovers of the solar system
In a preprint article (accepted for publication in Astronomy & Astrophysics), a team of astronomers from Leiden University in the Netherlands describe how they used sophisticated computer simulations to determine how the Oort cloud formed.
They took a new approach by starting from separate events that might have happened in the early days of the universe and connecting them together. This allowed them to map out the full history of the origins of the gargantuan cloud.
As explained in their press release, the scientists used the ending calculations from one event as the starting calculation for the next event.
Protoplanetary disk.Credit: Pat Rawlings / NASA
Their simulations confirmed that the Oort cloud is what remained of the protoplanetary disk of gas and debris from which it is believed our solar system formed about 4.6 billion years ago.
The cloud has comet-like objects made of debris from two places in the universe. Some of them are from nearby parts of the solar system, such as asteroids expelled by giant planets like Jupiter. Another group of objects in the Oort cloud comes from a thousand or so stars that were around when our sun was born, eventually drifting apart from each other.
"With our new calculations, we show that the Oort cloud arose from a kind of cosmic conspiracy," said astronomer and simulation expert Simon Portegies Zwart from Leiden University, adding, "in which nearby stars, planets, and the Milky Way all play their part. Each of the individual processes alone would not be able to explain the Oort cloud. You really need the interplay and the right choreography of all the processes together."
He added that the Oort cloud was ultimately produced by "the interplay and the right choreography of all the processes together."
As it is so far away, humanity hasn't yet built a telescope powerful enough to see the small, faint objects of the Oort cloud directly. By some estimates, it would take telescopes that are 100 billion times better than what we currently have to see into the cloud. Even the new James Webb Telescope that's launching later in 2021 is unlikely to be able to see that far, confirmed Nobel laureate (and James Webb Telescope scientist) Dr. John Mather.
It would also take humanity a long time to reach the Oort cloud. As NASA estimated, even if you consider that the Voyager 1 probe can cover about a million miles every day, it would take it about 300 years to reach the inner edge of the Oort Cloud. And to get all the way through, it would likely require another 30,000 years.
Does the universe keep extending endlessly into the abyss of space, or does it have a defined end?
Of all the scientific questions you may ponder, "Is the universe infinite?" is one of the hardest. It is impossible to answer with certainty at this point. Scientists have proposed both possibilities, and each has its own supporters and detractors. Determining whether the universe has some kind of boundary ultimately depends on figuring out its shape, size, and how much of it we can actually observe.
Is the universe infinite? And what shape is it?
The shape of the universe would have a lot to do with its size. Cosmologists have theorized that a universe would likely come in one of three possible shapes, which are dependent on the curvature of space. As described in Discover Magazine, the universe could be flat, having no curvature, but spatially infinite. Or it could be open, shaped like a saddle (with negative curvature) and also infinite. Or it could be closed, look like a sphere, and be spatially finite.
So which shape really is it? Nobel Prize-winning cosmologist John Mather of NASA's Goddard Space Flight Center, also the chief scientist for the James Webb Space Telescope, maintains that recent observations of cosmic microwave background radiation (CMB) remaining from the time of the Big Bang support the idea of the universe being flat, without any curvature (at least to the limit of what is observable).
"The universe is flat like an [endless] sheet of paper," shared Mather. "According to this, you could continue infinitely far in any direction and the universe would be just the same, more or less."
The geometry of the universe is determined by the density parameter Ω within cosmological Friedmann Equations.Credit: NASA / WMAP Science Team
Measuring the size of the universe
Current calculations say that the observable universe extends 46.5 billion light-years in every direction, making its diameter 93 billion light-years across.
Consider this: The age of the universe is 13.8 billion years, which means it took 13.8 billion light-years for the light from the farthest edge of the observable universe to reach us. But in that time, the universe has continued to expand at a rate that appears to be speeding up. Now, the edge of the observable universe has moved and is 46.5 billion light-years away.
That vast amount of space includes anywhere from 200 billion to 2 trillion galaxies, according to varying estimates. And each galaxy has, on average, around a 100 billions stars.
These gargantuan numbers are almost impossible to grasp. How did scientists come up with them?
As shared in an interview with BBC by Caitlin Casey, an astronomer at the University of Texas at Austin, scientists use a variety of tools and methods called "the cosmic distance ladder" to estimate distances between objects in the vastness of space. They start out with distances they can actually measure directly, like through bouncing radio waves off nearby bodies in the solar system, noting the time required for the waves to come back to Earth.
For distances that are harder to gauge, like those for galaxies at the boundary of the universe, astronomers utilize inferences based on calculations and observational evidence.
For instance, they employ "parallax measurement" that relies on measuring a star's shift in relation to objects in its background, as well as "main sequence fitting," which takes advantage of our knowledge of stellar evolution. (Stars evolve over time, changing size and brightness.) Knowledge of how brightness is connected to distance is paramount in determining the location of distant objects. So is analysis of redshift, which involves measuring changes in the wavelengths of light coming from faraway galaxies.
What about the unobservable universe?
If you notice, the numbers above pertain to the observable universe, the ball-like part of the universe that can be somehow seen from Earth or detected using our space telescopes and probes. But what about parts of the universe we cannot see? Some portions of the universe may be just too far away for the light emitted after the Big Bang to have had sufficient time to reach us here on Earth.
One study from a group of UK scientists estimated that if you take that into account, the actual size of the universe could be at least 250 times larger. They found that if you refer to space in terms of a so-called Hubble volume, which is similar to the volume of space in the visible universe, a closed and finite universe would contain roughly 250 to 400 Hubble volumes.
Another possibility entertained by scientists like Nobel Prize-winning Roger Penrose is that the Big Bang was just one of the periods of cosmic regeneration that our universe has experienced. There could have been multiple Big Bangs, followed by Big Crunches, periods in which a universe would stop expanding and collapse upon itself.
If all we know about the universe is derived from how it expands after the latest Big Bang, the questions if the universe is infinite or what size it may be are almost moot. As is often the case, more study and confirmation of our theories is needed.
Is there an edge to the universe?
Whether we have a finite universe or an infinite universe like an ever-expanding bubble, does it still have an "edge"? Is there some place you can go and say, "Yep, this is the end of the universe"? The simple answer is likely no.
As explained to LiveScience by Robert McNees, an associate professor of physics at Loyola University Chicago, the universe is isotropic. That means it follows the so-called "cosmological principle" and has the same properties and follows the same laws of physics in all directions.
If that is so, then the universe is much like the surface of a balloon. Imagine being an ant walking along a balloon. You wouldn't know there's an edge to it if you kept walking forward. You'd likely come back to where you started eventually, but the journey around and around could keep going without end.
If someone were to blow more air into the balloon as you keep walking along it, you'd experience some parts of the balloon moving farther away from you. Still, you'd be no closer to finding the balloon's edge.
Much like the ants, we're unlikely to get to the end of the universe. But we may still be able to answer one day "is the universe infinite" or does it have an actual boundary?
