In 100-Billion Years Accelerated Expansion –“Will Make It Appear That We’re Alone in the Universe”



If intelligent life re-emerges in our solar system in a few billion years, observes B. G. Buehler, only a few points of light will still be visible in the sky. What kind of theory of the universe will those beings concoct? It is almost certain to be wrong. Why do we think that what we can view now can lead us to a “correct” theory when a few billion years before us, things might have looked completely different?

If a far-future civilization were to look beyond our own future-galaxy, they’d see… nothing, continues Ethan Siegel in today’s Forbes. As the Universe continues on into the future, all the galaxies that aren’t part of our local group will accelerate away from us, owing to the presence of dark energy. Right now, those closest galaxies are around 10 million light years away, but the Universe is accelerating. When the Universe is double its age, those galaxies will be twice as far away; when it’s three times its present age, they’ll be four times as far away; at four times its age, they’ll be eight times as far away, and so on.


By time the Universe is an age of 100 billion years or so, the nearest galaxy to us will be about a billion light years away. The accelerated expansion of the Universe will make us appear that we’re alone in the cosmos.

One of the greatest dangers in all of science is jumping to false conclusions based on the limited data we have in our hands. We can never observe everything to arbitrary precision, so we’re always forced to extrapolate based only on what we do see. But what if the critical information that would lead us to the correct conclusion is exactly what we’re missing? This will be the case billions of years from now, when it comes to the Big Bang, and that frightening realization has led to a profound question from B. G. Buehler, who wants to know:

Let’s talk about what someone in the far future, say, tens of billions of years from now, would see.

There would still be hundreds of billions of stars in the sky, all accessible to whatever intelligent lifeforms arose with telescopes of the same caliber we have today. Some details would be different, however:

-there would be less dust and neutral gas,
-there would be a greater proportion of older, redder, lower-mass stars,
-there would be far fewer regions of active star formation,
and the stars would be distributed in a big elliptical halo, rather than in a Milky Way-like plane.

The main reason for all of this is that, over a time period spanning 4-to-7 billion years from now, the Milky Way and Andromeda, and eventually all of the local group galaxies, will merge together into one.

A series of stills showing the Milky Way-Andromeda merger, and how the sky will appear different from Earth as it happens. This merger will occur roughly 4 billion years in the future, with a huge burst of star formation leading to a red-and-dead, gas-free elliptical galaxy: Milkdromeda.

When major mergers like this occur, enormous amounts of new star formation occur, using up most of the gas and dust present within a galaxy. When a small region of very active star formation exists, we say there is a starburst occurring. When that region encompasses an entire galaxy, we label the entire thing a starburst galaxy. Very rapidly, those neutral atoms collapse to form new stars everywhere, but the most massive ones are very short-lived.

After only a few hundred million years, the more massive ones are all gone, leaving only Sun-like stars and the less massive ones around. By the time tens of billions of additional years have gone by, only the cooler, redder stars will remain. They may be dimmer, but there will be less dust to block their light in all directions.

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