# How long would it take to inhabit the universe?

Hello and thank you in advance.

I'm writing a hard science fiction story and part of it is how humanity is spreading throughout the universe. What I was wondering was, can anyone explain to me the equation needed to answer this question so the story can have it's realism?

In the near future, human beings created the very first wormhole that enables us to travel anywhere we want throughout the universe via spaceships. A gigantic internet of wormholes were generated through massive power inputs from solar energy harnessed and vacuum energy from space using a gigantic system of sophisticated lasers that utilize quantum non-locality to create the wormhole ins and outs regardless of distance throughout the cosmos. This may not make sense, but we don't need to get into that part.

At the same time, biologists figured out how to cure basically every disease known to humanity through stem cells along with infrared and EM rays that destroy cancer and viruses without harming other cells. New arms and legs (as well as other organs) are grown from stem cells also.

The stem cells have also enabled humans to live almost 1000 years where they keep replacing old aging cells with new ones from "fountain of youth stem cell" medicine derived from each persons own DNA, hence the medicines are unique only to each person.

Overpopulation is now a major threat to earth, and we are now able to terraform planets (such as Mars) to create greenhouse effects in the atmosphere or other gaseous atmospheres to suit our needs. In addition, we are also able to terraform stars in other solar systems to enable the stars to generate the gamma, theta, and ultraviolet light needed for life on the planets now terraformed in that solar system.

Ok, now for the equation I'd like to have. The wormholes enable us to take a spaceship or rocket ship to wherever we want in the universe in a matter of seconds, regardless of how many billions of light years distance there'd be. We can create these wormholes anywhere we want in the universe from any point we are at. If we're here on earth, we can create a wormhole from one point in the Andromeda galaxy to IC 1101 about a billion light years away, and so on and so forth.

If people are living to 1000 years each....... and they are reproducing 1 child every year...... hence, every 1,000,000 people are producing 500,000 children a year...... and they keep having children until they are 1000 years of age (women can have an indefinite number of ovums from the new stem cell medicine that keeps regenerating old cells back into new ones, thus, women are going through second menarche, third menarche, fourth menarche, etc. - basically no menopause), how long would it take for the population of one planet to go from 1,000,000 to 50,000,000,000 if everyone 18 years and older, including the new children when they grow to that age, reproduced one child every year? We're going to use 50,000,000,000 as the maximum number of people we can have on a planet on average.

When we've reached 50,000,000,000 people, we have to find another planet to live on since we're out of room. There are about 10,000,000,000 planets in the Milky Way that can be terraformed and inhabited since they are close enough to the stars in their solar systems for ease of terraforming. We send groups of 1,000,000 people to 50,000 newly-terraformed planets in our Milky Way. Now they're each reproducing one child a year amongst every 1,000,000 people on the new planets, 18 and older when the children grow up and all. When each of those planets have reached 50,000,000,000, they have to send their people to new planets again due to overpopulation. How long would it take before the entire Milky Way's 10,000,000,000 planets are fully inhabited? Don't forget, people don't live past 1000 years, so that's the only death toll we're going to consider - not murder, suicide, death from illness, etc.

We keep doing this until we've run out of planets in the Milky Way. We have to go to other galaxies, but the wormholes let us get there in a matter of seconds. Taking into consideration that each galaxy has an average of 10,000,000,000 inhabitable planets after they've been terraformed, and there are about 100,000,000,000 galaxies in the universe, how long would it take before we've inhabited the entire macrocosm? Again, we live to 1000 years each and everyone is reproducing children (a man and a woman, no cloning) from age 18-1000.

Yes, I know this is a very large equation and a complex one too, but I know an equation can be made. So the three questions are....... How long would it take for 1,000,000 to reproduce to 50,000,000,000 under the aforementioned conditions........... How long would it take for us to then inhabit the Milky Way under the aforementioned conditions........ and then the universe under the aforementioned conditions? Thank you much.

## Answers and Replies

Well, you're talking about geometric progressions, which can approach very big numbers very quickly. Say we get to the point where we double our reach every 2 years (Moore's law.) Start at 2 planets, then figure out how many times you need to double it to get to ten billion: 33. So if you double the amount of planets humans have colonized every 2 years: 66 years to fill the Milky Way. Yeah, seriously. That's the thing about geometric functions.

There are 100 billion galaxies so assuming that the Milky Way is average, in the total observable universe you would have 10^21 planets. You'd need 70 doublings for that.

So if humans go from Earth to Earth and Mars in 2 years, and can keep that rate of expansion, we'd have spread through the entire observable universe within 140 years. Less than one of your human's extended lifetimes.

You can recalculate base on how long you think it'll take for our species to double in scale, but unless we for some reason start progressing at a snails pace, you'll fill the universe very quickly, you'll still only ever need 70 doublings.

Ok, thank you much guys!

Human population now doubles in less than 30 years in several countries with high birth rate. So at that rate, 70 doublings to fill whole universe take 2000 years.
How much would birth rate change if women never die nor have menopause?