Did time begin at the Big Bang?

What do we know for sure about the early universe?

Distant galaxies are moving apart as the space between them stretches, so the universe was hotter and denser in the past. The whole sky also glows faintly with microwaves. This cosmic microwave background is leftover light from about 380,000 years after the Big Bang, when the universe cooled enough for atoms to form, according to NASA. In its first few minutes, the hot universe also made the lightest elements, and the predicted amounts agree well with what astronomers measure, says the Particle Data Group’s review, though lithium remains a puzzle.

In 2013, ESA released Planck’s map of the microwave glow, then the most detailed ever made; the data imply an age of 13.82 billion years, ESA reported. The hot, dense early universe about 13.8 billion years ago is Established.

Earlier than that, the evidence thins out. Many cosmologists think a burst of extremely fast expansion, called inflation, happened in a tiny fraction of the first second. But NASA says that scientists aren’t sure what came before inflation or what powered it. Inflation is supported, but still debated.

Was the Big Bang an explosion in space?

No. The word “bang” suggests a bomb going off in an empty room, with matter flying out from a center. A NASA astrophysicist explained instead that the Big Bang “occurred everywhere all at once,” with no location anyone could point to. It was the start of an expansion that is still going on (NASA, Ask an Astrophysicist).

An analogy helps. Picture raisin bread rising in an oven. Every raisin moves away from every other, and none is the center. Galaxies are the raisins; the dough is space. Where it breaks: a loaf has a crust and sits in an oven. The universe has nothing like the crust, and no known outside room to expand into. The same NASA page adds that if a larger space did hold our universe, we might never be able to measure it.

Why can’t physics rewind all the way to time zero?

In the 1960s, physicists proved the singularity theorems. Using general relativity, they show that the universe has a finite past in a broad range of models, as the Stanford Encyclopedia of Philosophy explains. In the standard models, trace matter backward and you reach an edge the equations cannot cross: the singularity, where density becomes infinite.

So did time begin there? Not necessarily. The theorems say little about what that edge is like, and general relativity leaves out quantum effects, which should matter most in that tiny, dense state. Any account of what came “before” needs a deeper theory. Even within Einstein’s theory, the entry notes, the standard models have no first moment, because the idea of time itself breaks down as you approach the start. An analogy: the numbers bigger than zero have a lower limit, but no smallest member. It describes the math, not what really happened.

Inflation does not escape the problem. In 2003, Arvind Borde, Alan Guth and Alexander Vilenkin showed that a universe that has been inflating, or just expanding fast enough, cannot extend forever into the past, so inflation needs other physics at its boundary (Physical Review Letters). That does not prove time began. It moves the question one step back.

The strongest objection: maybe there is no “before”

In a 1996 lecture, Stephen Hawking argued that if nothing before the Big Bang could ever affect what we observe, we might as well say time began there. That is a choice of description, not proof that nothing came before. And even if time did begin, a question remains: why did it begin in this particular state? The Stanford Encyclopedia lists the early universe’s smoothness and flatness as puzzles that any theory of the start must explain.

What might have come first?

The first four ideas come from professional physicists. None is confirmed.

A true start with no edge

In 1983, James Hartle and Stephen Hawking proposed the “no-boundary” idea (Physical Review D). In Hawking’s plain description, the universe begins at a point like the North Pole: an ordinary point, not a singularity. A common summary: asking what came before is like asking what lies north of the North Pole. Hawking called it a hypothesis to be tested. In 2017, one team argued that the math does not deliver the smooth beginning the idea needs (Feldbrugge, Lehners and Turok); Hartle and colleagues replied that a properly defined version does (Diaz Dorronsoro and others). In 2018 the first team answered that the fix still fails (Physical Review D).

A big bounce

Loop quantum gravity is one attempt to join gravity with quantum physics. Applied to simplified model universes, it replaces the Big Bang with a “big bounce”: an earlier universe shrinks to a tiny but finite size, then expands again (Ashtekar, Pawlowski and Singh, 2006). If so, time did not begin at the Big Bang, but these are simplified models of an unfinished theory.

Cycles and colliding branes

In 2001, four physicists proposed that the hot Big Bang began when a brane, a membrane-like world in a higher-dimensional space, collided with another surface (the “ekpyrotic” model). Paul Steinhardt and Neil Turok then built a cyclic model of endless eras, each beginning with a bang and ending in a crunch (Science, 2002). Roger Penrose has proposed a different cycle, in which each era grows out of the one before. In 2010, he and a colleague reported rings in the microwave sky as traces of an earlier era, but independent teams found that ordinary random patterns in the glow produce the same rings (Moss, Scott and Zibin). That claim is Not supported.

A branch of a larger multiverse

Some versions of inflation never fully stop, so our universe’s “start” would be a branch point off a larger multiverse. The Stanford Encyclopedia entry’s authors warn that if everything happens somewhere, any observation fits, which makes the idea hard to test.

Author’s hypothesis: a ripple from a larger space

Ricardo Maldonado, author of GOD PLAYS DICE, proposes an idea called HD-Blast, short for higher-dimensional blast. In Chapter 2 of the book he pictures our universe as the surface of a pond whose depth the fish cannot see. Something violent happens down in that depth, and the fish feel only a wave racing across their world. In his proposal, our hot beginning is that wave, set off by a brief blast in a larger, higher-dimensional space. The analogy breaks down fast: a real pond sits inside space and time, while this idea is about where they came from. It is an unconfirmed Author’s hypothesis. The book says any such model must still produce the expanding universe we see, nearly the same everywhere and in every direction. It names a possible test in the faint hum of gravitational waves, ripples in space and time, that pulsar-timing arrays search for, using spinning dead stars as clocks. Details are in the author’s public Zenodo record, which is not peer review.

Where can people of faith and skeptics agree?

Augustine of Hippo, who lived from 354 to 430, wrote in his Confessions that God made time along with the world, so asking what God did before creation misses the point: “there was no then when time was not.” He also refused to mock people who ask such deep questions, saying he would rather admit he did not know (Confessions, Book XI).

In 1931 the Belgian physicist Georges Lemaître, a Catholic priest, argued in Nature that quantum theory suggested a beginning of the world very different from nature today. He did not use his science to argue for his faith. When a 1951 speech by Pope Pius XII seemed to suggest that science proves creation, Lemaître raised his concerns with Vatican officials, and the Pope’s 1952 speech to the International Astronomical Union avoided that claim, a University of Navarra history reports.

Here is common ground. On physics alone, a first moment would not show what, if anything, caused it, and a bounce would not rule out a deeper cause. The Stanford Encyclopedia notes that physical theories of the origin push the question of why the universe exists back a step rather than answering it. That part is Beyond science. And everyone can share the measured facts: the universe was hot and dense about 13.8 billion years ago, and nobody yet knows what, if anything, came before.

How can you check it yourself?

• In NASA’s short history of the universe, find where it says scientists aren’t sure what came before inflation.
• Look at ESA’s Planck map. It shows the universe at about 380,000 years old, not at time zero.
• Read section 3 of the Stanford Encyclopedia entry “Philosophy of Cosmology” on where Einstein’s theory stops.
• For any claim about “before the Big Bang,” including the author’s, ask three questions. Which model is this? What does it predict that the others do not? Has an independent team checked it?