By Emily Levesque, University of Washington
In astronomy, we regularly find ourselves asking questions that are so profound that they can almost seem absurd. Where did the universe come from? How will it all end? These two questions might seem ridiculous from a scientific perspective, but they’re actually very compelling astronomical topics, and physics gives us the tools we need to craft real answers and test new theories in painstaking detail.
Coining a Universal Term
The two questions about our universe are also deeply intertwined. Both deal with what our universe is made of as well as the physics of how everything interacts, how we see it changing with time, and what lies ahead. When asking questions this big, it’s good to start by being very clear on what we mean. So, to start, we’re going to define what we mean by the universe’s beginning and end.
Georges Lemaître was the Belgian priest and astronomer who first proposed the idea of an expanding universe. He then extrapolated this idea back to the beginning of time, noting that an expanding universe must have expanded from some initial moment or starting point.
Years later, the English astronomer Fred Hoyle was describing this theory during a radio interview and summarized it by saying, “All the matter in the universe was created in one big bang at a particular time in the remote past.” Hoyle himself didn’t support the theory at the time, but with that interview, he unwittingly coined the term that would go on to define this widely accepted theory for how the university began—the Big Bang.
The Universe and the Singularity
The Big Bang itself describes that first initial instant, the moment when the universe first burst into being from an infinitely dense and hot primordial point, known as “the singularity”. At the instant of the universe’s birth, this point began to expand, ballooning from impossibly, infinitely small into the beginnings of what we now know as the entire universe.
If you think this is sounding a bit like science fiction, or even poetry, that’s understandable. The laws of physics themselves make it very hard for us to study that initial beginning point of the universe. However, even in the tiniest fractions of a second after the Big Bang, physics does allow us to begin describing our new and evolving universe.
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The Beginning of the End of the Universe
Where we think the universe came from and how it got to what we see today matters a great deal when we try to project forward to where it’s going. Those initial moments that drove the formation and expansion of the universe will continue to influence the evolution of the universe and its ultimate end.
Will it keep expanding forever? If it does, will that expansion eventually rip the universe apart or cause it to slowly drift apart, fading and cooling into oblivion? Or will this expansion slow down, stop, and maybe even reverse? Will the universe eventually careen back inward in a reversal of the Big Bang, ending in a big crunch and a new singularity? These are exciting and compelling questions, but they are also incredibly hard to answer!
Fortunately, astronomers today have the tools we need to develop and test theories that reach as far back as the beginning of time and as far forward as the end of everything. With cutting-edge telescopes, astronomers can measure how the universe is moving and expanding today, measuring how quickly galaxies are moving away from us, calculating the Hubble constant, and testing whether those data are consistent with a universe that’s getting ready to crunch back together or tear itself apart.
Peeking into the Past
This might seem strange because it isn’t obvious that looking at the universe today would tell us much about its earliest beginnings, but this is where the speed of light is on our side. Observing very distant galaxies is like looking back in time since light emitted millions or billions of years ago is just now arriving at Earth.
Studying those galaxies’ properties and how they move helps us to fit the pieces of the universe that we study into a puzzle that changes with time, and studying those changes tells us how the universe has evolved. We can also use that same principle—the speed of light and observations that act like time machines—to peer as far across the universe and as far back in time as we possibly can, detecting light from some of the earliest moments of the universe.
The cosmic microwave background is the faint radio-wavelength glow of the light emitted in the earliest epochs of the universe, and the properties of that background act as fingerprints of things that happened even earlier in the universe’s beginnings. By combining these observations and everything we know about the laws of physics, we can begin to answer questions that may have once seemed impossible to address.
Understanding the earliest moments of the universe means understanding how we got from the primordial singularity—the seed of the Big Bang—to the vast web of spacetime containing the planets, stars, and galaxies that we see today.
Common Questions about How We Can Answer Big Astronomical Questions
English astronomer Fred Hoyle was trying to explain the concept of the universe starting from an infinitely small point and expanding outwards. He said, “All the matter in the universe was created in one big bang at a particular time in the remote past.”
To answer how the universe will end, we have to first understand how it began because how the universe started and what happened in its earliest moments affected its expansion, and understanding that will give us an idea of how the universe will end.
The speed of light works in our favor to answer how the universe began. Because of the speed of light, when we observe distant celestial objects or distinct galaxies, we are seemingly looking back in time since the light that these objects emitted millions or billions of years ago is just now reaching us.
