Ask Ethan # 53: What is the Big Break?

The most terrible of all the fates of the universe, leading to the complete destruction of all that was and will be

Why is it necessary to be so lonely? So many people live in this world, each of us is eagerly looking for something else in another person, and still we remain as infinitely distant, separated from each other. Why is this supposed to be? For what? Maybe our planet rotates, feeding human loneliness?
- Haruki Murakami

Around us there is a huge universe, stretching for hundreds of billions of light years, containing at least a trillion galaxies. It is possible that the Universe, whose dimensions exceed the observed part of it, is infinite. But what will happen to her in the future? Among your excellent questions and suggestions sent this week, Jeff Harris's question was asked to answer in our column, asking:

I once read an article in the New York Times about something called the Big Break. They pointed out that the accelerating expansion of the Universe would lead to the fact that galaxies could not interact with each other, atoms could not form, and matter would “evaporate”. Considering the current expansion rate, is such an outcome possible? What will be the main stages of this Big Gap, and after what time from the current they will occur?

If you are interested in the fate of the universe, you need to go back to the Big Bang and follow how it developed to this day.


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In its early stages, 13.8 billion years ago, the universe was hot, dense, almost perfectly homogeneous, and expanded very quickly. Since the Universe is very massive, a gravitational attraction acted in parallel to it, slowing down the expansion, opposing it, and possibly able to reverse it. The latter depends on three things: the initial rate of expansion, the total amount of matter and energy in the Universe, and the type and proportions of the types of energy present.

For a long time it was believed that the universe has three options for development:

1. when there is enough matter and energy to overcome the initial expansion, it will slow down, stop, and go backwards. The universe collapses into a big compression
2. when there is not enough matter and energy, and the expansion will continue indefinitely. Gravity will slow it down, but it will always be positive, and distant galaxies will continue to be removed.
3. the perfect balance between these two options, when another proton would have led to a recollapse, but we do not have it. In this case, the expansion rate will asymptotically tend to zero.

Of course, the real universe behaves differently.



It expanded and slowed down for a very long time, while matter and energy eroded, and then, about six billion years ago , the speed at which galaxies flew away from us ceased to decrease and the Universe began to accelerate. This acceleration continues now, without any signs of slowing down.

Although the density of matter and energy continues to fall, the ongoing acceleration tells us about the existence of a new form of energy, in addition to the usual ones: the one we call dark energy.



Dark energy expresses itself in various observations, including large-scale structures, microwave cosmic radiation, while observing distant objects — gamma-ray bursts, quasars, type Ia supernovae. Over the past years, we have measured it very carefully, and over the past 10 years the measurement error of its amount has decreased from 100% to 8%.

Given our limited capabilities, we believe that dark energy is indistinguishable from the cosmological constant — that is, its density does not change with time.



But it does not have to be an exact constant. Theoretically, the best hypothesis (with the least amount of assumptions and free parameters) is the assumption that dark energy is a cosmological constant. Of all the possibilities, this would be the least surprise.

But there are others - dark energy can be almost constant, decreasing from a larger value in the past, albeit slowly. In this case, the phenomenon of acceleration would also gradually disappear, with the result that the Universe would cease to expand at all.

It is also possible that the dark energy will change from a positive to a negative value, and will lead to a large compression.

But there is another option - what Jeff wants us to consider - that dark energy will increase with time. This will lead us to the Big Break.



If dark energy were constant, then an object located 10 million light years away would have to move at a speed of 150 to 200 km / s. By the time it turns out to be 20 million light-years, its speed will be 300 km / s. With a distance of 100 million light years, the speed will be 1500 km / s, with a billion light years it will be 15,000 km / s, and with 20 billion light years it will be equal to the speed of light, 300,000 km / s!

But since the Universe is already accelerating, and there are already objects moving away from us at a speed greater than the speed of light, it turns out that 97% of the surveyed part of the Universe — stars, galaxies, planets — are no longer available to us forever. Even if we jump into a starship with an unlimited source of energy today, we will not be able to reach them.



If dark energy is constant, then the Solar System, our galaxy and a local group of galaxies — including the Milky Way, Andromeda, the Triangle galaxy, Magellanic clouds, and a couple more dozen dwarf galaxies — will remain gravitationally bound for trillions of trillions of years in the future. But if it grows or increases, then the acceleration will not only take away distant galaxies from us, but also destroy the gravitational bonds of these structures!



If the density of dark energy increases tenfold relative to today's value, the Milky Way will no longer unite with Andromeda, but, on the contrary, disperse with it, like all distant galaxies of the Universe. Triangle Galaxy and most others will also be lost.

If you increase it 100 times, the stars from the edge of the Milky Way will begin to scatter, and the metric expansion of space will overcome the attraction of all matter in our local group. Increase it by 200-300 times - and even the sun will fly away from our galaxy.



And if the density of dark energy continues to grow, what will happen to our solar system? As a result, the planets will fly away from the Sun, and the Earth will be thrown out of orbit when the density of dark energy increases - get ready - 100 billion times. In the end, and people will overcome gravity, as well as cells, molecules, atoms and nuclei will be broken, if the density of dark energy will increase to infinity. Perhaps even the space-time itself will burst at the end.



A terrible fate, of course. It was first described in 2003 by Robert Caldwell, Mark Kamionkovsky and Nevin Weinberg, and everything was pretty simple for them. All forms of energy density in the Universe have pressure associated with them, and it (with the help of some unit transformations) can be expressed in terms of density. For stationary dust, the pressure is zero, for radiation, the pressure is equal to 1/3 of the energy density, and for cosmological constants, the pressure is equal to a negative value of the energy density.

In physics, we call the constant going first (+1/3 for radiation, 0 for matter, -1 for the cosmological constant), the parameter w, and we call it the equation of state. The authors of the term “Big Gap” considered w to be -1.5, and found that the Universe will end in 22 billion years. Almost all the events described above will happen shortly before the end, and then the density of dark energy will have to increase very slowly, and in the end start to increase sharply to infinity.



Based on today's observations, we can set w = -1.0 with an error of ± 0.08, with the result that the Big Gap moves 80 billion years back from today. If you want to calculate the lifetime in the case of any of the variants of the equation of state, you can substitute it in the following formula. Just be sure to convert the units correctly.



Keep in mind that, as far as we know, w = -1, and then it turns out that there won't be a big gap. I would bet on it if I were a gambling person, although it is important to remember that this is all science, and we do not rule out any possibilities - no matter how unpleasant they may seem to us, as long as the evidence allows.



Thank you for the smart question, Jeff, and if you want your question to be covered in our column, send it to us. The universe is full of mysteries, large and small, worthy of reflection.