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Let's imagine a story where the "aliens" leave a lot of super-advanced technology somewhere in the solar system. Scientists spend years excavating this technology and while it seems too advanced for us -eventually it helps to progress our level of civilization. However, after years of research, scientists have a hard time finding out who the aliens really are.

Then, in a plot twist, we learn these are actually future humans from another universe. They came here not just for a "roadside picnic" but because their universe has more life than our own...in their version of the Solar system they had intelligent life on Mars and Venus (the composition of these planets is much different, as with their sun), and that means they were constantly attacked and exploited, not just by intelligent life but also many alien bacteria from other worlds.

So while we struggle to find ANY life in our Galaxy (even microscopic extremophiles) they had contact since antiquity with other civilizations (some were peaceful and didn't intervene with their development). With the invention of the radio, they heard messages from other star systems far and wide. When they progressed to the space-age, they even found some primitive lifeforms on the moon.

With all these lifeforms that existed on almost every planet-and in most star systems-many big empires emerged that were fighting each other. At the end of the XXII century, Earth almost lost a war that destroyed most of humanity. This is why they think our universe is much safer, and theorize that life must be extremely rare here.

Now, we are talking about alternative evolution here..the alternate universe has different laws of physics and life is much more common.

So...do we have any theoretical idea of what needs to be done with the laws of physics to make life more common? Tweaking certain laws, making stars closer or farther from each other, you name it.

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    $\begingroup$ (a) Asking if something fantastic "if feasible" is not a good idea, especially in your title. Especially when it's not really what you're asking. I recommend deleting everything after the ellipsis in your title. (b) The help center has a rule called the "book rule." In short, any question that would be reasonably answered with a book-length answer is out of scope for all of Stack Exchange - in other words, the question is too broad. This one feels that way. Either there's too many issues that would need to change or the "issue" would lead to too many complications. (*Continued*) $\endgroup$
    – JBH
    Commented Apr 18, 2023 at 14:06
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    $\begingroup$ To @KalMadda's point, just declare your physics somehow different, and don't explain or justify it otherwise. $\endgroup$
    – Tony Ennis
    Commented Apr 18, 2023 at 20:29
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    $\begingroup$ I think it's a nice question - don't let one user's opinions convince you otherwise. Also don't sweat the "you don't need to care about the science" comments - you don't have to, but you have every right to care about if you want to. $\endgroup$
    – N. Virgo
    Commented Apr 19, 2023 at 0:01
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    $\begingroup$ You can make life more common without changing any physics. Just choose a setup with a greater abundance of resources like food. $\endgroup$
    – Wyck
    Commented Apr 19, 2023 at 2:38
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    $\begingroup$ @Wyck food as we know it comes FROM life.. it isn't a natural resource in itself before life happens. Unless you mean something different than most people by food. $\endgroup$
    – coppereyecat
    Commented Apr 19, 2023 at 14:27

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The Great Filter isn't so great.

https://en.wikipedia.org/wiki/Great_Filter

This is more ammunition for your thinking than a real solution, because "the real solution" requires picking one or more of your favorite Great Filters and finding a way to simply remove them. It isn't very scientific because we don't actually know which of these "great filter" candidates may be the one that has really caused the universe to be so quiet, so the choice is yours. The upside is no one can tell you that you're wrong because we just don't know. You'll be pleased to know that people have been thinking about this a lot, though.

e.g. if we assume that the leap to "single cell life" is the Great Filter -- the step which almost no planet anywhere gets past -- then you just fix that. Once every planet, moon, and asteroid is teeming with single cell life, the floodgates are open beyond that. (You can do a deeper dive into that particular filter and see what the theories are for why it might be The Great Filter. It is all speculation, however.)

Or if you assume that "the great filter" has to do with star/planet formation, then you work out a way to fix that. Perhaps there's a different balance between gravity and dark energy and this results in much more even distribution of matter, resulting in far more stable "medium" creations (e.g. rather than giant stars that supernova and kill everything within 50 light years, or black holes and all their effects, perhaps this other universe has some built-in tendency to settle into nice medium weight stars and stable planetary orbits).

So the solution is up to you, but "The Great Filter" is your list of possibilities. (The Wikipedia list, as it states, is by no means complete, but it's a start.)

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    $\begingroup$ Thanks for the reply,the wikipedia article is very helpful.I guess i can use your idea of diffrent dark matter propotions when the scientists in the story will be trying to figure out how the other universe works.They can have a general discussion about the size of the stars and dark matter,and will come with some general theories about diffrences between both universes. $\endgroup$
    – Mishima
    Commented Apr 19, 2023 at 7:08
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Feasible

Can I have a universe with X?

Yes you can! If anyone tells you otherwise, tell them their argument fails because they are using the logic of this universe. Your other universe has different logic. You get to decide the logic. So you get to decide if there is more life or not. Blam!

So...do we have any theoretical idea of what needs to be done with the laws of physics to make life more common? Tweaking certain laws, making stars closer or farther from each other, you name it.

No!

In fact, we do not know how to explain the formation of life in the real universe, in terms of physics. Trying with fictional universes is a waste of effort.

Don't start with the weight of a proton and the falloff rate of the electroweak interaction. Start with the fact that life is common. Don't worry about what this means for fundamental physics.

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    $\begingroup$ I've gotta admit... hallelujah, brother. $\endgroup$
    – JBH
    Commented Apr 18, 2023 at 16:54
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    $\begingroup$ Amen. I would go a step further - we don't know the relationship between the known laws and constants of our universe, so we can't predict if changing any of them in isolation is even a concept that means something, although it's sometimes fun to play with the possibility. $\endgroup$
    – g s
    Commented Apr 18, 2023 at 17:58
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    $\begingroup$ Good answer. And don't explain or justify what's different. Something is. Just write your story. $\endgroup$
    – Tony Ennis
    Commented Apr 18, 2023 at 20:30
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    $\begingroup$ Glory, glory! It should also be pointed out that if this situation existed, it would take hundreds of years of thousands of scientists from every domain of knowledge from both universes collaborating to compare and contrast the differences between the two in order to figure that out. Understanding the fundamental forces of our own single universe is already a centuries-long struggle that myriad Ph.D. holders are grasping after $\endgroup$
    – automaton
    Commented Apr 19, 2023 at 14:15
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    $\begingroup$ @automaton Sounds like the ultimate world building project for one to to squirrel away and avoid writing one's novel. $\endgroup$
    – Daron
    Commented Apr 19, 2023 at 15:16
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Thier Universe had a a Progenitor Race, Ours Did Not

A progenitor race is a common trope in science fiction that a intelligent race existed before mankind. In your other universe, some intelligent species beat mankind to the stars by millions of years and seeded the whole galaxy with life. Because of thier tech level, they could terraform countless worlds like Venus, Mars, etc. to be more hospitable to life, and places to inhospitable to terraform could be met half way with genetic augmentation. Over time, this race would fragment into countless empires, evolve into many distinct alien races, and see many worlds abandoned by intelligent life, colonized again, genocided, recolonized, then abandoned... millions of years is a long time after all.

Since it only takes 1 intelligent race coming before humanity to make this all happen, the entire difference could be as simple as a single asteroid impact. Imagine if the dinosaurs in both worlds were on the verge of space flight, but our world get the Chicxulub impact, and thier did not. So the physics and chemistry of your universe could be the same and predicated on the idea that the evolution of complex life is rare, but the amount that life has spread to date could be very different.

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    $\begingroup$ Conversely, ours has a progenitor race.... a really really xenophobic, unfriendly one. I recall a sci-fi short story where basically this was the case, and they seeded the galaxy with kinetic launchers tuned to look for intelligent radio signals. As soon as one was detected, it launched a mass at the target at 99% the speed of light. $\endgroup$
    – JamieB
    Commented Apr 19, 2023 at 0:58
  • $\begingroup$ @JamieB I considered that option too, but I think this version works better because it explains why places like Venus and Mars are livable, in thier universe whereas in ours these planets are very hostile places. A Dark Forest explanation would be a very good fit at a galactic scale, but is more problematic at a local solar system scale. $\endgroup$
    – Nosajimiki
    Commented Apr 19, 2023 at 16:27
  • $\begingroup$ This was pretty much the same option I was thinking of: the medium-to-long-term result of an ancient race colonizing the galaxy, then eventually fragmenting and descending into low tech levels, would look very much like the question premise. Honestly the hard part is how to actually have (remotely recognizable) humans show up... $\endgroup$
    – January First-of-May
    Commented Apr 21, 2023 at 13:25
  • $\begingroup$ @JanuaryFirst-of-May Earth could be a nature reserve for the progenitor race. If they evolved here, they may have done something special to protect this world allowing evolution to follow a similar course after they left, or if they evolved somewhere else, a rare world like this with "other evolved life" may have been worth preserving like an endangered animal's habitat. Perhaps Earth has some sort of Ancient planetary auto-defensed system that has prevented our Venusian and Martian neighbors from interfering in our affairs? $\endgroup$
    – Nosajimiki
    Commented Apr 21, 2023 at 15:05
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Focusing only on how to increase the likelihood of life and not on how to overcome problems like FTL travel between star systems...

As I mentioned in my comments, the basic chemistry leading to life is already at its maximum in the universe — at least insofar as we understand life today. If your story is only considering carbon-based lifeforms then the problem isn't convincing the universe that it wants more life, it's convincing it to provide more places to allow life.

We call the range of distance from any particular star that is most likely to host life as we understand it the "Goldilocks zone." Planets aren't too hot or too cold. They have a high likelihood of nitrogen/oxygen rich atmospheres and liquid water. (Again, focusing on carbon-based life, which we are beginning to understand, and not on life based on other elements, which we don't understand.) This is just one variable of many that constitutes a planet that has a high chance of life.

Therefore: I propose your universe has a higher percentage of just the right planets in just the right places

In your universe, there are a lot of Earth-sized planets in the Goldilocks zone of most stars. Those planets have an abundance of chemistry that will lead to liquid water. This might also mean your universe has a higher distribution of stars likely to have life (let's say a lot of stars like our own, loving, yellow-dwarf sun).

I recommend that you completely ignore how this change in distribution came to be. The physics of solar system construction is only just being understood by humanity, but two things we do understand a bit better are the probability of mass forming into systems like ours and the mass requirements to do so. Your universe's Big Bang would have to be something quite different from what we believe ours to have been like — and I think that's a rabbit hole with little excavation value.

In fact, the idea of finding life on, insofar as we know, moons and planets that can't support life represents so great a divergence from the known universe that it would be hard to rationally and believably explain. At least I think so. Life on the moon? What did it eat? How did it survive the solar wind? Even bacteria needs food and a permissive environment. So I'm recommending sticking with planets that today's science thinks can host life.

But, since we're willing to cheat at the casino of the universe a little, we might as well be all-in...

I'm a fan of Johnny Worthen's Coronam series of books. Well, I'm a fan of the first book, "Of Kings, Queens, and Colonies.* I only recently bought the second book. But you can use a similar plot construct to what he did.

The Coronam solar system has eleven planets and a gap where a twelfth would be, all balanced in the same orbit. Consequently, all of the worlds are inhabitable (and most are). Let's ignore the gap and say the twelfth planet is there. The author created a fictional world that met his needs and not one that demonstrated physics. But the point is... this is plausible.

(BTW: It's worth searching this stack. Questions about the idea of multiple planets sharing the same orbit has been asked a fair number of times.)

So, in your universe, the probability of multiple planets sharing an orbit in the Goldilocks Zone is much, much (much) higher.

To be honest, your story might be better if you used this plot device rather than creating Galactic Empires. You wouldn't need FTL to plausibly have the wars you're talking about. Just a thought.

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    $\begingroup$ You could tamper with ideas similar to how the range of the habitable zone could be extended - either make sure all rocky planets accrete atmospheres and keep them (many levers to manipulate) or go down the simplistic dimensionality route - Flux conservation in a 2-D universe would imply the radiation flux from a 2-D star decreases as $F\propto r^{-1}$, which would make the equilibrium temperature of planets decrease like $T_{\rm eq}\propto r^{-1/4}$, as opposed to $T_{\rm eq}\propto r^{-1/2}$ in our universe. This way, you would have an extended habzone. $\endgroup$
    – AtmosphericPrisonEscape
    Commented Apr 18, 2023 at 15:26
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    $\begingroup$ +1 for the excellent answer, and another +1 for the excellent phrase "a rabbit hole with little excavation value" $\endgroup$
    – GuilleOjeda
    Commented Apr 18, 2023 at 21:19
  • $\begingroup$ Great idea with multiple planets on one orbit-didn't know that something like this was in any way possible.I didn't specifically mean carbon based life,as im positive that Titan could have non-carbon life.However i guess that i will focus on carbon based life,as i want beings from another universe to spread viruses and fight each other over terrain (so it is better they will have similar biology) .So the "more planets in goldilocks idea" is good.FTL will be possible in both universes of the story,but will be limited (i will ask another question soon about the subject).Thanks for your reply ! $\endgroup$
    – Mishima
    Commented Apr 19, 2023 at 7:01
  • $\begingroup$ @Mishima multiple planets in the same orbit per se isn't possible. Well, you could have a gas giant and two terrestrial planets at its L4 and L5 Lagrange points, but I don't think that would be stable over geological time periods. You could also have a gas giant with multiple habitable moons, or a habitable terrestrial planet with a habitable moon. It's also possible to have multiple planets on different orbits all within the habitable zone, as at Trappist-1. $\endgroup$
    – N. Virgo
    Commented Apr 19, 2023 at 12:58
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    $\begingroup$ @N.Virgo While you may be right (the universe surprises astronomers and physicists almost daily), please remember where you are. Worldbuilding is a site for creating imaginary worlds (see the help center). We're not physics-lite. The goal is to create suspension of disbelief by rationalizing everything from the improbable to the impossible. We underscore that by pointing out the futility of membership in the Religion of Science: the blind belief that what we understand of science today is the only understanding there will ever be. If the OP agrees, in his/her universe, this is real. $\endgroup$
    – JBH
    Commented Apr 19, 2023 at 23:50
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I'm going to focus on "How could it come about?"

When trying to understand the "special circumstances" that allow Earth to harbor life, the thing you hear over and over is that Earth has life because it has numerous protections against radiation. The strong magnetic field is well understood, but there is also a thought that the pulses of inertia and diversity in Earth's history of life might be due to our passing through areas where nebulas block the galaxy's core.

So, let's imagine a universe where the universe is subtly opaque to high-energy radiation. Not so much that the Earth doesn't receive it's life-giving sunlight, but enough that the solar wind doesn't strip Venus's atmosphere of hydrogen, and Mars might be able to hold an atmosphere for longer.

This allows life to form in places where it would currently be scoured by ultraviolet light. It means that a supernova wouldn't cleanse nearly as large an area.

If you wanted to properly balance the laws of thermodynamics, you'd have to figure out what happens to that energy, but that would be the subject of another question.

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Earlier life formation

You could use a non-sentient progenitor race.
Just say a 'small' amount of organisms (some bacteria?) came into existence very early into the universe's formation through some fluke. These were so hardy that some of them could survive the terrible conditions. They spread along with the universe's expansion, multiplying as they spread. Eventually, some found their way to nearly everywhere where life was possible.
(I imagine humanity discovering some of the bacteria frozen in the middle of some asteroid)

From thereon, evolution is sure to follow. whilst sentience may not always evolve, just having many more places where evolution is happening at a moment makes the chances of sentient life evolving larger. Larger than not having a 'seed of life' everywhere.

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  • $\begingroup$ I like this answer, because it points to the fact that life on Earth developed fairly "late" on the galactic timescale. It's not much of a stretch at all to ask "What would have happened if life arose a billion years earlier?" $\endgroup$
    – Nate Barbettini
    Commented Apr 19, 2023 at 16:16
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There is theoretical life that was proposed to live in atmosphere of Venus, above the sulfuric acid clouds. There is theoretical life proposed to life in Martian soil and underground. Europa is another example I'm sure I don't need to introduce to anyone. If you look just at what people speculated is possible and not at what we have actually found, then the solar system could be brimming with life. So to answer your question - nothing has to change in laws of physics for the solar system to be full of life.

One more thing about Venus: You might already know, that Venus in it's early history had liquid water and was not much different from Earth. It has been speculated, that had life formed on Venus, dead organisms would accumulate carbon in the planet's crust and take it out of the atmosphere, thus preventing the greenhouse effect that makes Venus far hotter than it ought to be if you only consider the distance from the Sun. If Venus had the same atmosphere as Earth, it would be habitable by humans unlike Mars, which barely reaches average high temperatures above freezing.

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This is something of a frame challenge, though only a very minor one and I hope it's helpful.

We don't actually know what leads to the origin of life. Some people think it requires very specific chemical conditions while others think it's easy and happens all the time. It's hard to tell because the origin of life happened so early in Earth's history that there just isn't any evidence left that we could examine. There are lots of people working on the problem, but for the moment we just don't have any idea how it happened or how easy it was.

This means that for all we know the origin of life is ridiculously easy - leave any organic chemical soup lying around for a few million years and you'll come back to find little microbial critters swimming around in it.

But wait, you say: if that's the case then why don't we find life on Mars and Venus and all the other bodies in our solar system? Well, take your pick. There's something about our universe that picks those microbes off just as they're getting going. Maybe that's some kind of mysterious force, or maybe it's just that our universe has lots more meteorites and solar flares and so on - things that can unbalance a fledgling ecosystem and send it on the path to total extinction. Either way the other universe doesn't have it, and that's why life is so much more common there.

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Minor frame challenge: what if life is more common only in the solar system? Ie. don't worry about the whole universe.

It would be easier to justify.

Suppose humankind's technological development in the other universe had progressed only slightly faster for tens of millennia. Due to laws of exponential growth over long periods of time, they would easily have had our level of technology a thousand years ago. So, they would have been capable of inhabiting other planets (and moons) already for hundreds of years. They would have also brought bacteria around everywhere, in exotic environments, giving them chance to evolve into something we have never seen, for example.

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“Where life is more common; is that feasible?”

Yes, in an alternate Universe, you have pretty much complete liberty as a writer. Your alternate universe could even have alternate physics. It’s literally your world to decide what you want to do with.

Would it be plausible?

Yes, it could be very plausible. In an alternate Universe with more worlds in the Goldilocks Zone, this would mean more worlds that could support life. And certain forms of life can expand very rapidly.

As the writer, you just need to sell it

This is somewhat of a frame challenge, but this is my answer for you. Because you are dealing with an alternate universe, you have pretty much complete authorial liberty. Just make sure and sell it well to your readers. Explain that life grows and replicates at a higher rate in this alternate universe. Perhaps twins/triplets are far more common in this universe, and are actually the expected norm. You’ve got this.

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It might be abundant in our universe

We actually do not know if life can be abundant or not. That we haven't found it yet, doesn't mean our universe cannot be teeming with life, or will be teeming with life.

If we suppose our current universe can be teeming with life, we can talk about many kinds of big filters. For example, some science suggests that we can be one if the first intelligent life in the universe with a chance to go to the stars. The universe was incredibly chaotic and dangerous before, with beams from stars and black holes basically sterilising the galaxy periodically.

Your alternate universe doesn't need much change to have more life. It might just be a bit more old than our universe, offering enough life to evolve. Or another filter is a lower barrier, allowing life to happen more easily. Thus it is teeming with life when humans happen to come to the scene. Mars, as an older planet that used to be more hospitable than Earth would have that head start, as long as they survive the drastic change later. It could even be that life on Earth started because of unsanitised space probes crash landing on Earth.

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Alternative thinking: The future is ours.

Expanding universe = smaller [accessible] universe (in future)

Our universe is 'expanding'. Meaning, things keep moving farther from each other. So much so, that there are far off regions moving farther so fast that even light (universal speed limit) can't reach us back, ever. That is the boundary of our "observable" universe.

ref https://youtu.be/uzkD5SeuwzM

As time goes on, our (from ~ Earth) observable universe (and reachable universe) will be "smaller", because everything would have moved far enough away to not matter.

At this point, universe would be only our galaxy and some surrounding neighborhood galaxies. In this future universe, life could be abundant, more common.

Why?: Given time (from now to then), more life might pop up here and there and expand. Also, since it'd be a smaller universe the ratio of life instances to visible stars would be higher. => more common life.

So for your future 'humans' life would seem more abundant in the universe (their visible universe) and also more crowded perhaps.

The past is empty and vast

Now, they can't travel faster than light to get far away themselves. What's the next best thing? travel to the past! - Terminator style.

They appear in the past somehow, and end up at the present (or past) Earth Solar System. Seeing sooooo many more stars visible and such a large universe, with barely any life started, they decide to help humanity have an early start.

Of course , being humans we can be so self destructive/quarrelsome as to send ourselves back to stone ages again and again forgetting our discoveries of radio waves or any outward looking tech. So they decide to leave the really high grade tech somewhere hidden in solar system, so we are advanced enough to sustainably move past our planet first before we find it.

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  • $\begingroup$ nothing moves faster than light in the physical universe, it only APPEARS to move faster than light. That's the nature or nature. From EVERY POINT in the universe everything APPEARS to move away from you at an ever increasing rate. This of course is physically impossible, but that's the nature of how things work. $\endgroup$
    – jwenting
    Commented Apr 20, 2023 at 8:51
  • $\begingroup$ True. Nothing moves faster than light in vacuum of space. But the underlying space of the universe itself expands. The speed limit doesn't apply to space, more technically speaking speaking space itself doesn't have a speed (anything moving over it does). In the end though, the effect is the same. Visible universe will decrease over time given continuation of currently observed behavior. Feel free to edit the answer if you feel there's better wording that will convey the idea. :) $\endgroup$
    – nine tales
    Commented Apr 21, 2023 at 19:05

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