How old is it? The Universe, of which our galaxy (the Milky Way) is a tiny portion. What does it look it like in its formative stages, the billions of years ago theatre of stars, planets and galaxies that miraculously came into being?
In this post, I do two things. First, I explain how through ingenious methods, scientists arrived at the age of the Universe, a number that virtually all astronomers and astrophysicists agree. Second, I report a new simulation of the Universe unfolding from close to the time of the Big Bang. The simulation is the latest and most comprehensive effort to date to peek at the Universe in its “baby” stage, utilizing the massive firepower of the world’s most advanced supercomputers.
The Age of the Universe
Let’s imagine ourselves in the role of a physicist wondering about the age of the Universe and through some simple means, arrive at a consensus estimate of that age. When we look out to objects in the distant cosmos, we are looking back at their past. Because light travels at a finite speed, the light from a distant object that we see now had to be emitted long ago. Astronomer Edwin Hubble (1889-1953) – mentioned in yesterday’s post – observed that the patterns of starlight that distant galaxies emit – their spectra – are shifted toward longer wavelengths, compared with the light patterns of closer galaxies. This is the redshift. The farther a galaxy is from us, the larger the redshift. In more detail, Hubble discovered his eponymous law which states that the size of the redshift is proportional to the distance, which implies that distant galaxies are moving away with speeds proportional to their distance from us.
If we imagine reversing the galaxies’ motions to reconstruct the past, then that proportionality acquires dramatic new meaning. In reversed flow, the more distant galaxies will be moving toward us more rapidly, covering the distance such a way that everything converge or began together at the same time. Thus, we are led to the notion that at the beginning, all matter in the Universe was packed together much more tightly than it is today. Essentially, this backward simulation leads to the Big Bang, when all matter and energy was packed into a tiny ball known as the singularity.
When did this happen? To calculate how long ago, we simply divide the distance a galaxy must travel by the speed at which it is moving. Since a galaxy’s speed is proportional to its distance, we’ll find the same result consistently whichever galaxy we choose (that’s the beauty of immutable physical laws!). Doing that, initial estimates picture that galaxies were all stuck together along 20 billion years ago. More accurate calculations, which include how the velocities change over time due to gravity, yield a somewhat smaller number. Today’s best estimate of the Universe’s age, measured from the time of the Big Bang, is 13.8 billion years.
When we look back 13.8 billon years or so, all the way to the Big Bang, we reach the limits of our vision. The initial explosion during the Big Bang was so bright that we are “blinded by the light” and we can’t see beyond it and so for now, this early episode belongs to the realm of religion and metaphysics. All scientists can say with certainty is the visible Universe has a birthday. It is finite.
The Size of the Universe
Knowing the age of the Universe also gives us an idea of its size. Here is where the idea of measuring distance in light-years really shines. Since the limiting time is 13.8 billion years, the limiting distance is, well 13.8 billion light-years! To bring the immensity home, consider the fact that the earth’s radius is “only” about one-billionth of one light-year. So, the Universe is immense indeed and our visible “world” is large. There’s plenty of room for humans to observe, wonder, speculate, test theories and write poetry about.
The Shape of the Universe
As mentioned, recent simulation using very powerful computers have given astronomers a fresh and up-to-date picture of how the “lumpy” stuff of the Universe – things like stars and planets – came into being. To my mind, these scientific simulations are more exciting than any regular computer game! Here are a few worth watching.
Here’s a video showing a simulation developed by MIT scientists showing the time evolution of dark matter structures in the Universe.
And now, the largest and most realistic simulation of the universe to date – the Uchuu simulation developed by an international team of scientists using the world’s most powerful supercomputer dedicated to astronomy. Here’s a short capsule video of this massive effort.
For more details of the Uchuu simulations, and a longer video, visit this website: