Is the universe old or young?

I’d say it’s old, from the perspective of sentient intelligent life on Earth, as it seems to be a long shot that we’ll ever find others. The galaxies and stars just too far away. Only a small fraction of the stars that we do see are even theoretically accessible, and that number is shrinking. If sentient, intelligent life is very rare, which appears to be the case (we only know of 1 example out of the billions of species of life that we know to have existed), then the universe might be too old to find any others.

But from the perspective of the universe itself, which has no inherent desire for life to flourish or even exist (we’re just accidents, or the equivalent of a tiny infection under one of the universe’s fingernails), the universe is quite young.

I thought it was Last Thursday

This is the same logic that I struggle with knowing that I am alive just 6000 or so years since the start of human civilization.

I am not firm on the logic of this…but it just seems wrong. If humanity will exists for a long time then why am I HERE just 6000 years from the start.

Same with the universe.

I can’t help thinking that maybe…maybe…I don’t know…but that it isn’t that weird because humanity will not last that long and so may be the same with the universe. Maybe, just maybe intelligent life has a very short time to arise and that happens to be about now. Maybe the universe is unstable? Vacuum decay? Maybe something just makes it unstable and it will change to a version where people can’t wonder about such things.

Idk…just pondering :slight_smile:

Voyager 1 is the furthest away human object at 14 billion miles. I’m sure someone could do the actual scale to put it into prospective, but ISTM that when we try to understand the universe from our available information it’s like we are ants trying to make predictions about what life is like in Milwaukee based on what washes ashore near our colony in New Zealand.

There are still many nebulae left out there, which means there are still many stars that aren’t even born yet. On the other hand, if scientists are correct and the universe is at least 12 billion years old, you’re no spring chicken, either, so you can’t really be young. I’m thinking that, in human terms, it is in its mid to late twenties.

Ahhh, the Doomsday Argument, which comes from taking the Mediocrity Principle too far!

I am no expert on this, but as I understand it, here is how the argument goes.

Given no other evidence, we should assume that there is nothing unusual about our situation.

If you pull a bead at random out of a bag full of beads and it is red, and you are allowed to pull no other beads from the bag, what do you conclude about the other beads? Well, you have slightly more reason to believe that they are red than any other color. It is possible that they are multicolored with red, white, and blue beads in equal proportion, and this isn’t terribly unlikely. It is also possible that 99.999% of the beads are white and yours was the only red one, but again, this is unlikely compared to the possibility that many beads are red and you happened to pull out a common red one.

If you pull out another bead and it is also red, the idea that red beads are common seems more likely (though it IS possible that you have now removed the only two red beads in the entire bag full of white beads). On the other hand, if the next bead is yellow, your assessment of the possibilities should change.

Where does the Doomsday Argument come in? Well, you are alive and thinking about this. You were born to your parents and are who you are, but that is by chance. You could also have been born in Hawaii, or Saudi Arabia, or to the Queen of England. You could have been born in 2022, or 1950, or 43,000 BC. Your conciousness could have belonged to any human that ever lived or will live, but by chance, you are you.

So essentially, youe conciousness pulled a life to live out of the bag of all humans that have ever lived, and guess what? You are alive today, when the human population is higher then ever. Around 7% of all people that have ever lived were alive in 2020, according to a quick Google search.

If we all die tomorrow, the Earth explodes or something, then that 7% would represent all humans who have ever lived or will live. Picking a life at random and being in that 7% doesn’t seem too unlikely.

On the other hand, if humanity lives on for another 30 billion years and colonizes the galaxy, then the bag of all human lives is many orders of magnitudes larger. Quadrillions upon quadrillions of humans. And what are the odds that you’d be one of the infintensimally small fraction of humans alive tosay? Not 7%, but 0.000000…%.

So the Doomsday Argument states, we know we are in the group alive today; it is more likely that this represents a common state for human lives rather than an infinitesimally uncommon state; therefore, humanity will not live on for eons and number in the quadrillions - it will be wiped out soon.

The problem with this logic is that it always applies. If the first band of Homo sapiens could comprehend this principle, they’d rightly conclude that it is enormously unlikely, per the mediocrity principle, that they are lucky enough to represent the first few thousand humans; and that it is far more likely that the species will soon go extinct rather than numbering in the billions in the future.

Of course, one could argue that from the perspective of the universe itself, “old” and “young” don’t mean anything. The universe does not, from our current understanding, seem to be cyclical. It just is; it expands, and always will. There is nothing experiencing time to compare it to; time and space, intertwined, are what the universe IS. A human can be said to be old or young in the sense that time affects a human, and a person’s age can be compared to other people, or to things that are much shorter or longer lived than a human. a human is a passenger in time and the universe. The universe itself is not.

Like this idea.

"Theoretically, over an extremely large but not infinite amount of time, by sheer chance, atoms in a void could spontaneously come together in such a way as to assemble a functioning human brain.

“The Boltzmann brain gained new relevance around 2002, when some cosmologists started to become concerned that, in many theories about the Universe, human brains in the current universe appear to be vastly less likely than Boltzmann brains will be in the future”

The future being like 10^10^69 years.

This boggles my (possibly Boltzmann) brain!

And if vacuum collapse happens, we’ll never know.

I once watched an episode of either How the Universe Works or PBS Spacetime (can’t remember which) in which the scientist stated the the universe went through more changes in its first second of existence than it has since, or ever will…They were also discussing the need for Planck time to lay out these very early changes, since they happened so fast. So I guess based on that, it’s old?

You went through more changes in the first 9 months since you were concieved than you have since, does that mean a 1 day old baby is “old”?

Agreed, but the other problem with it is that it assumes that we are special by being us. If all the beads in the bag are going to be pulled out, then someone’s going to get the rare bead. It is only when that person thinks that they are already special before they get that rare bead that they now have any reason to believe that the selection meant anything profound.

If humanity lives another trillion years, we were still here, we had to be here, and it is only our ignorance of the future that makes us think that our place in time is special.

It may be that we are the last generation to walk the Earth, and there are number of doomsday scenarios that make that increasingly likely. But I’ll agree that the doomsday argument has never been one that I thought compelling in any way.

ETA: this bit got ninja’d by @Babale

A human goes through far more transitions in its development before they are born than they will the rest of their lives, and by the time they are a teen, they really only have a couple of “eras” left. By this standard, a 13 year old would be said to be most of their way through their lives.

It’s easier to look at eras, as they can be counted much easier than the years that go by between eras, but I don’t know if it’s as relevant to this question.

To the OP, I would vote young, but mostly mature. It’s like a 13 year old that can look forward to living 10,000 healthy productive years, and then still spend some millions (or more) after that in retirement.

Never mind

Wait a minute, you can’t “never mind” something that you never heard in the first place. So, you have to post what you were going to say so I can “never mind” it.

I thought the quotes would disappear as well. It was my mistake to post a reply without reading all the subsequent posts to see that the topic had already been addressed. I was posting that in terms of a potential age of 10^40 years or so, that comparing the universe to a human puts as at the stage where the sperm just barely met the egg, not someone in who is in their 20s.

Right. That’s been a thought I’ve had about the Fermi Paradox, too. “We see no spacefaring aliens; it is monumentally unlikely that we would be the first spacefaring species if intelligent life is common; therefore intelligent life must be incredibly uncommon”.

Sure, the logic checks out. But in a hypothetical universe teeming with alien civilizations, you know who would have also found the logic completely sound? The first alien civilization on the scene!

Your “10 to the 40th” number shocked me, so I did some research. I haven’t run into anything remotely that long in terms of its projected life span. In fact, I found this seemingly outlandish assertion taken from a paper submitted in 2010:

“The universe will cease to exist around the same time our sun is slated to die, according to new predictions based on the multiverse theory.”

Yes, Wolfpup posted this a few days ago. It seems to be nothing more than an extension of the Doomsday argument to the entire universe. In other words, nonsense that relies on taking the Mediocrity Principle too far (as Babale pointed out).

I was going by this post, and picking a middle number in the range of how old the universe might get should proton decay be something that happens.

I’ve always thought that the Fermi Paradox was something like Zeno’s paradoxes, in the sense that it’s more of an intellectual exercise than something that we need to actually explain. In the real world, isn’t the explanation that any intelligent life being able to travel outside it’s own solar system is impossible from a practical standpoint, so that no matter how much time we have the numerator in how likely we are to get to another solar system is zero. IMHO two civilizations meeting each other will only happen is in those rare cases where there is more than one planet or moon in the same solar system that develops intelligent life.

That can’t be right! Google, here I come!

How many stars are born in the Milky Way? Star formation within the Milky Way currently involves about 4 solar masses of gas condensing into stars each year. Since the average star is less massive than the Sun, astronomers believe the Milky Way is producing roughly 7 stars per year

Lord, it is pathetic! If stars last ten billion years or so, and so few are being born every year, then our universe should be writing its last will and testament as far as being a viable entity.

Our Galaxy is replacing 0.000000000000175% of its stars every year. :flushed:

Nah, I don’t think that’s the case. Getting to the next star over at a fraction of light speed may take hundreds or thousands of years, and once you colonize one system it might be thousands more before your colony is developed enough to repeat the process; but if an alien civilization had evolved halfway across the galaxy around the same time the dinosaurs went extinct and has been expanding since then, they’d have been here (and everywhere else in the galaxy) by now, even at the glacial pace of each colony sprouting off another once every few thousand years.

Let’s say this civilization colonizes a new planet in 10,000 years; after 10,000 years of development, both the home planet and colony send off new colonization ships, and 10,000 years later the process repeats.

After 40,000 years, we have 8 colonies. By 100,000 years, there are 512 colonies.

After 300,000 years we have 537,000,000 colonies.

After 1,000,000 years we have 6.338×10^29 colonies. Which I think is more stars than there are in the observable universe?

And that’s only 1/65th of the time they’d have had if they accomplished spaceflight when the dinosaurs were wiped out.

Exponential Growth is a hell of a drug.