Overpopulating the Milky Way Galaxy Exponentially

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LesPhelps's picture
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Overpopulating the Milky Way Galaxy Exponentially

In the Crash Course, I like the stadium / magic water drop example of exponential growth.  

A similar example I ran across was calculated by Tom Murphy.  He calculated our energy growth exponential curve into the future.  His milestones were when we would require the entire energy output of Sol and when we would need the entire output of the galaxy.  Here's the link:


I was commenting on our out of control population growth recently and began to wonder where that would lead us... with no resource constraints.  Specifically, I began to wonder how long it would take us to overpopulate the Milky Way Galaxy left unchecked.

So I started with a variation on Drake's Equation:


N = S * f * n


N = The number of planets in our galaxy inhabitable by humans

S = The number of stars in our galaxy = 300 billion

f = The fraction of those stars that have Earth size planets = 1/6 (NASA)

n = The fraction of planets that can support human life or be terraformed = 1/2 (liberal parameter)


Then I calculated the number of people it would take to max out the habitable planets:


M = P * N


M = Maximum human population in the Milkyway

P = The maximum number of people per Earth like planet = 7 Billion


M = 2.5 Billion * 7 Billion = 1.75E20

Finally, I plugged an equation into a spreadsheet starting with 7 billion people in 2013 and increasing the population by 1.1% per year (the 2009 CIA estimate for world population growth).
And the magic year came out to be 4202 AD.  In approximately 2,192 years at 1.1% population growth we can overpopulate our one and only galaxy. Not even SciFi dreams large enough to allow us to travel to other galaxies.
I made a comment recently that I bet it would take less than 2,000 years to overpopulate the galaxy.  Based on the above assumptions, I was premature by 192 years.  Why didn't anyone call me on it?
BTW, I am aware of Dyson Spheres and ring worlds.  However, I've already givem humanity unlimited resources and free faster than light travel.  I feel I've been more than generous with my assumption gifts.laugh
jerryr's picture
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Posts: 157
Not even wrong....

Since you're already aware of Dyson Spheres, you know what you need to do.

LesPhelps's picture
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Posts: 830

Yes I do know what I need to do, nothing.  I'm not growing the population.  If other people can't moderate their procreation, they can build the spheres!

gillbilly's picture
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Joined: Oct 22 2012
Posts: 423

 NSFN= No Sex For Now

M= PN, Must Procreate Nomore

Sorry, I couldn't resist.wink

Someone posted on the other thread that procreation is like food and it won't change. last time I checked we had an obesity problem as well.

Arthur Robey's picture
Arthur Robey
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Joined: Feb 4 2010
Posts: 3936
I'm getting boring.

I'm getting boring.

We have to gain access to the fabric of our own being. We have to redesign what we are. We are developing the tools to do that now.Genetic engineering and very powerful quantum computers and programs that learn from their mistakes.

Darwin's slow process of natural selection will have to be done in the virtual world, and the results implimented in the real world.

I anticipate that the result will be that we have to make the process of pregnancy and procreation as voluntary as lifting an arm and no more compelling.

Then any unlawful procreation can be sanctioned, as it will be completely an act of will.

But I anticipate the results of the virtual evolutionary process. I am getting ahead of myself.

I find that many arguments start from basic assumptions that things will be more or less the same as they are now. Not even close.

Any niche left by someone deciding not to breed will be filled by those who are sublimely indifferent to their situation.

All of this is carefully told in my sci-fi The Breeding.

LesPhelps's picture
Status: Platinum Member (Offline)
Joined: Apr 30 2009
Posts: 830
More is always better

Interesting that obesity was mentioned in this topic.  There is a simpler concept than the exponential function that is not understood by humanity and it's also a major contributor to our dilema.  The word "enough" is simply not understood or considered.  Adequate is another word that is not employed when it comes to purchasing or consumption decisions.

Speaking of scifi, I know of at least two books where advanced alien races threaten to eliminate or contain homo sapiens if they attempt to take their violent nature into galactic space.  If any advanced alien races exist, I expect they are just as likely to take unkindly to humanity expanding into space with uncontrolled population growth.

I remember reading about Thomas Jefferson talking to Clark about the Lousiana Phrchase, saying that it would take 5 generations to expand across that vast a space.  One generation later we had largely expanded into the purchase.  We are just like algae blooms.  We rapidly increase in numbers to consume any available resources at our disposal.  As a species, we don't seem to employ any cognitive control over our expansion, either in numbers or individual consumption.

Actually, I believe I was overly generous with my assumptions regarding habitable planets.  I don't believe there are anywhere near 3.5 billion uninhabited habitable planets in the Milky Way.





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