We Might Be Alone in the Universe

[Dr. Shades]

That wouldn't be a problem if an advance civilization is slowly expanding, or if an A.I. probe is inside another probe.

How would an A.I. probe inside another probe change anything Res Ipsa said?

Voyagers 1 and 2 will orbit another star system in the far future, shouldn't we expect to find dead alien probes near the Earth?

Then why don't we?

[Physics Guy]

How will the Voyager probes end up orbiting another star system? Were they even aimed at one? If not, there is really a lot of space between stars. On the scale where a star is the smallest dot you can make with a pencil, and a solar system fits on a tabletop, stars are mostly spaced several miles apart. Probes launched at random into interstellar space will probably never come close to any other star.

Even if the probes were aimed at some other star system, gravitational capture is tricky. It requires either a fluky kind of three-body interaction, or friction. Otherwise an incoming probe that approaches another star will just speed up under the star's gravity, and slow back down again as it leaves. It will end up having its trajectory deflected, but it won't be captured into orbit. Gravity is not velcro.

Our solar system will only have collected alien probes that were aimed at us specifically, and that were specifically built to stop here on arrival, by decelerating with retro-rockets or a solar sail or something. Whatever the method, it will probably more than double the difficulty of launching the probe, because the task of decelerating into our system is the exact mirror of the initial problem of launching out of the home system, plus the probe now has to include its deceleration solution with it when it is launched. It's not clear why an alien species would go to that significant extra trouble just to leave an artefact for us to find, when for much less effort they could probably make a probe that would pass close to many systems and send back data on all of them.

[Gadianton]

DT,

My assessment of the government UAP reports is close enough to Kippings. However, that wasn't really my point about UAPs. My question is how Dr. Kipping is going to confirm a UAP is from an alien civilization?

[Res Ipsa]

Speculation about a necessary connection between our sun/solar system and the ability for life to form is insufficient to let us lower the number of planets with life significantly.

You are missing the point. Nobody is rejecting the possibility of life forming in many star systems. However, if life is possible everywhere, why do we happen to be in a very unusual solar system? Perhaps we are just lucky to be in a special solar system, but we don't know that.

You're jumping to the conclusion that specific characteristics of our solar system significantly affect the formation of life on a given planet based on very limited evidence or speculation. Physics Guy already covered this. You're also committing the lotto fallacy. The odds that intelligent life occurred in our solar system, regardless of how you choose to characterize it, are 1-1. You're simply stating the Weak Anthropic Principle, which does not support the conclusion you are trying to draw.

I really recommend you watch this video,

"Is the Solar System Special?" by exoplanet researcher Dr. Kipping
https://www.youtube.com/watch?v=-ixuftVYC5o

I don't do videos. Has Dr. Kipping published a paper on the subject?

References:
1. Jupiter-like planets in Jupiter-like orbits are uncommon.

"Our results are consistent with the literature, i.e., that Jupiter-like planets in Jupiter-like orbits are relatively uncommon, occurring around less than 10% of stars."
https://iopscience.iop.org/article/10.3 ... X/819/1/28

So, we're going to play the lift a single sentence out of a paper game and treat it as if it's established fact. I'd hoped you'd learned by now how unreliable that is if you are interested in drawing supported conclusions. So, the data comes from the Anglo-Australian Planet Search. What is that? Well, it's a project to search the brightest stars visible from the southern hemisphere to look for planets. The original target sample was about 200 stars, including F, G, K and M class stars. http://schwab.tsuniv.edu/papers/apj/hd1 ... eprint.pdf That's a minuscule, non-random sample of all the stars in our galaxy -- let alone the universe.

The paper you cite starts out with the context in which it is written:

Much attention has been brought to bear in recent years on the occurrence rate of Earth-like planets (e.g., Wittenmyer et al. 2011a; Howard et al. 2012; Kopparapu 2013). This is due in large part to the flood of data from the Kepler spacecraft mission, which has provided evidence that small planets are exceedingly common (e.g., Dressing & Charbonneau 2015; Fressin et al. 2013; Burke et al. 2015).

Given the limits of technology, the first exoplanets discovered were giants, leading to speculation that earth-like planets are rare. But with technological advances leading to better quality instruments, we learned that small planets are "exceedingly common."

Now, if we are interested in finding other intelligent life, we have to deal with the fact that we have a sample size of one. Us. So, where should we look? Given limited resources, which of the trillions of stars in our galaxy should we spend resources on? Well, one reasonable search strategy would be to focus our efforts on solar systems with characteristics similar to ours, as the one thing we know is that intelligent life developed in our solar system. But that's not anything like having sufficient information to conclude which of the many, many different features of our solar system are necessary for, or even preferable for, the development of life. The reasoning you are following is something like: we know the life developed in our solar system. Therefore, life can develop only in solar systems like ours. That's fallacious reasoning, unless you have access to reliable data on a large number of solar systems as to which actually have developed life and which haven't.

The paper continues:

These findings are a critical step toward answering the fundamental question "how common are planetary systems like our own solar system?" However, to fully understand the degree to which our solar system is unusual, we must also consider the other planets therein. In other words, how common are planetary systems that feature distant giant planets such as our own gas and ice giants (Jupiter, Saturn, Uranus, and Neptune).

In fact, the AAPS changed its original survey plan to concentrate on finding Jupiter analogs. Again, as a search strategy, that makes sense. The paper cites good evidence that Jupiter played a significant role in the formation of our solar system as we observe it today. What it doesn't attempt to answer is the question: is the presence of a Jupiter analog in the solar system necessary or even beneficial to the formation of life in a solar system. In fact, the paper is actually a test of a computer simulation that attempts to account for the problems in detecting Jupiter analogs, using prior estimations for comparison. That's what the paper is about: it is not about "how rare is intelligent life in the universe?"

2. There's no Super Earth in the Inner Solar System.

"a significant majority of the long-period gas giants identified in RV surveys of field stars likely host inner super-Earths."

https://iopscience.iop.org/article/10.3 ... 881/aaf57f[/quote]

Again, you lifted a snippet without reading and understanding the paper. You even failed to read the definition of the term "super-Earth" as used in the paper.

In this study, we examine 65 super-Earth–hosting stars, where we define a super-Earth as a planet having either a mass between 1 and 10 M⊕ or a radius between 1 and 4 R⊕, depending on the detection method.

The lower bounds of the definition means that there is no significant distinction between earth itself and a "super earth" as defined in the paper itself.

The paper says nothing about whether the presence or absence of a super earth among the inner planets of a solar system has any effect of the odds that life will develop in that solar system. Once again, you are making an assumption that has nothing to do with what the paper is about. What is the paper about? Here's the conclusion:

We find that super-Earth systems appear to have more gas giant companions than we would expect to see by chance alone, even after accounting for the additional uncertainty introduced by our inability to pinpoint the precise locations of these companions for systems with RV trends. The high occurrence rate of long-period (>1 au) gas giants in super-Earth systems in turn implies that a significant majority of the long-period gas giants identified in RV surveys of field stars likely host inner super-Earths. We therefore conclude that the presence of an outer gas giant does not hinder super-Earth formation, as proposed in some previous theoretical studies. To the contrary, our data suggest that these companions may either actively facilitate super-Earth formation or simply serve as a fossil record of early disk conditions that were particularly favorable for planet formation over a wide range of semi-major axes.

So, the presence of an outer gas giant in a solar system doesn't hinder the formation of inner super earths, with the lower bounds of super earths being planets of essentially the same mass or radius as Earth's. The paper says absolutely nothing about the likelihood of intelligent life forming in other solar systems. It simply rebuts a theory about the effect of gas giants in a solar system on the formation of inner planets similar in mass or radius to earth or larger.

3. Only about five percent of stars are solar-like. To make things crazier, "The Sun is less active than other solar-like stars". That means only about 0.5% of stars are truly sun-like.
https://ui.adsabs.harvard.edu/abs/2020S ... R/abstract'

Same problem, only worse. You reached a conclusion opposite to that suggested by the paper. Here is the full abstract:

The magnetic activity of the Sun and other stars causes their brightness to vary. We investigated how typical the Sun’s variability is compared with other solar-like stars, i.e., those with near-solar effective temperatures and rotation periods. By combining 4 years of photometric observations from the Kepler space telescope with astrometric data from the Gaia spacecraft, we were able to measure photometric variabilities of 369 solar-like stars. Most of those with well-determined rotation periods showed higher variability than the Sun and are therefore considerably more active. These stars appear nearly identical to the Sun except for their higher variability. Therefore, we speculate that the Sun could potentially also go through epochs of such high variability.

The paper does not conclude that there is some essential difference between our sun and other solar-type stars. It suggests that our sun could also go through periods of variability similar to those of other solar-type stars. The abstract does not examine the effect of the observed differences on the likelihood of life forming in the solar systems around the other stars. Again, this is an observation of 369 stars with a very limited ability to gather specific information about the stars.

If you multiply points one, two, and three, you get a very improbable solar system. If Jupiter was essential to the formation of life on Earth, then that could suggest that life is rare.

Yes, you could multiply. But it would be GIGO. You haven't established any relationship between the characteristics of our solar system you focus on and the likelihood of the formation of life. You also use "rare" without thinking through what that means. Even if solar systems with identified characteristics of our solar system are "rare," that leaves billions or trillions of solar systems materially indistinguishable from our own. That still heavily favors the development of life many places in the universe.

Also, if your thesis is that life "could be" "rare", then the bulk of your post is unnecessary. You're equivocating on where the goalposts are.

In addition, as Everybody Wang Chung posted, the expansion of space itself makes a large percentage of the universe both inaccessible and unbearable to us. And that expansion is accelerating. There is a huge number of planets for which we would be forever unreachable by probes.

That's true, good point!

If it is, why do you ignore the implications?

It depends on what the OP is asking. If “alone” means the only intelligent species that exists in the universe, I’d say the sheer numbers of possible planets in the universe makes intelligent life anywhere at any time a near certainty.

Nobody knows the probability of life. For all we know it could be 1 in 10^50.

We could be alone in the Universe, but intelligent alien life could exists in other universes, do you deny that possibility?

Given the number of stars in the universe, the presence of life on Earth is inconsistent with that "possibility." We have no reason to believe that. Given the reasonable proposition that we should not assume that the Earth is in some kind of privileged position with respect to the formation of life, it is much more reasonable, based on what we know, to conclude that we are not alone in the universe.

If your argument is as you state it, then your entire post is a waste of time. The substance of your argument appears to be that it is more likely than not that we are alone. Again, equivocation on where you are setting the goalposts.

The claim that probes would travel at near-light speeds ignores the problem of increasing mass as speed increases. That the probe itself experiences time dilation doesn’t change the time it takes the probe to move from one star to another relative to the two stars. So, the speed of light remains a hard speed limit.

That wouldn't be a problem if an advance civilization is slowly expanding, or if an A.I. probe is inside another probe.

Voyagers 1 and 2 will orbit another star system in the far future, shouldn't we expect to find dead alien probes near the Earth?

The slower a civilization expands, the less likely it would be to find an alien probe orbiting the earth. As time passes, the Earth becomes beyond the reach of more and more star systems.

You'll have to explain the relevance of probes within probes to the speed limit imposed by the speed of light. I don't get it.

Physics Guy has already addressed your evidence-free assertion that the Voyager probes will end up orbiting another star system.

So the fact that our sun is magnetically calmer than a lot of stars is not really a separate fact from its being larger than all the many small stars—it's just a consequence of that same fact.

Extremely few other stars are going to be exactly like our sun, but any star with close to its mass, and around roughly its age, will be quite similar to it. The moderate scarcity of G class stars, among all stars, is just an indication of how common it is to have around a solar mass and be somewhere in stellar middle age. Somewhere between 5 and 10% of stars are G class. It's a fuzzy number because it's hard to know how many of the smallest stars exist. Small, cool objects are hard to see, and if you can see them, it can be hard to be sure whether they are stars or large gas planets.

There are still an awful lot of stars like our sun out there. nce on transiting, terrestrial exoplanet astronomy is polling with sampling fractions around or below a few percent, and a strong bias for small orbits.

The Sun is unusually quiet compared to other type G2 stars. There are many stars out there, but how many stars are a quiet type G2 star with a Jupiter-like planet, but no super Earth in the inner orbit?

I would like your opinion on the papers I linked to.

You don't need a physics expert to evaluate the papers you linked to. You could do it yourself if you stopped lifting snippets out of them and trying to build an argument on the snippets.

[Philo Sofee]

I look at it like Steve Hartman does on Friday Night news, On The Road on CBS (my very favorite time of the news). We have more than enough people here on this planet we can be kind to and spread love. Why worry about whether we are alone or not? We AREN'T alone, we all have each other right here. Looking out into the night sky misses the actual togetherness we all have and can enjoy. Why not re-focus right here at home on this earth, our lovely home, instead?

[doubtingthomas]

The odds that intelligent life occurred in our solar system, regardless of how you choose to characterize it, are 1-1.

That's not what I am saying. I am simply wondering why we live in an unusual solar system. Is it because
A) We are very lucky to have an unusual solar system.
OR
B) Life is not possible in the vast majority of solar systems, so life here is just the result of a selection effect.

Given the number of stars in the universe, the presence of life on Earth is inconsistent with that "possibility." We have no reason to believe that.

Sean Carroll said, "Life could just be rare. Probability of life starting could be 10^-100 per planet. We just don’t know ". If the probability of life is 10^-100, then alien life in our universe would be effectively impossible.

However, string theory allows for 10^272,000 universes. The number of stars in our universe is nothing compared to 10^272,000. There could be an infinite number of universes. So, it's possible we are alone in our universe, but alien life existing in other universes.

It suggests that our sun could also go through periods of variability similar to those of other solar-type stars.

That's possible, but wouldn't those periods be very unusual?

So, the presence of an outer gas giant in a solar system doesn't hinder the formation of inner super earths, with the lower bounds of super earths being planets of essentially the same mass or radius as Earth's. The paper says absolutely nothing about the likelihood of intelligent life forming in other solar systems.

That's not the point I made there. I am simply trying to demonstrate that our solar system is unusual. It's probably a good thing that Mars or Venus are not a Mini-Neptune.

So, were going to play the lift a single sentence out of a paper game and treat it as if it's established fact. I'd hoped you'd learned by now how unreliable that is if you are interested in drawing supported conclusions. So, the data comes from the Anglo-Australian Planet Search. What is that? Well, it's a project to search the brightest stars visible from the southern hemisphere to look for planets.

Here's what the paper says, "From a sample of 202 solar-type stars, and correcting for imperfect detectability on a star-by-star basis, we derive a frequency of ${6.2}_{-1.6}^{+2.8}$% for giant planets in orbits from 3 to 7 au...Our results are consistent with the literature, i.e., that Jupiter-like planets in Jupiter-like orbits are relatively uncommon".
https://iopscience.iop.org/article/10.3 ... X/819/1/28

The majority of stars are red dwarfs, solar-type stars are brighter than red dwarfs.

I know the 202 sample is small, but I doubt the Astrophysical Journal would accept papers that have useless samples.

[doubtingthomas]

t's not clear why an alien species would go to that significant extra trouble just to leave an artefact for us to find, when for much less effort they could probably make a probe that would pass close to many systems and send back data on all of them.

Interesting! What do you think about Sean Carroll's tweet? And why don't we see evidence of expanding civilizations? Isn't the galaxy old enough to have been colonized by at least one intelligent civilization?

[doubtingthomas]

We should keep in mind that our limited ability to detect exoplanets skews the data away from planets like ours.

This paper states, "From a sample of 202 solar-type stars, and correcting for imperfect detectability on a star-by-star basis, we derive a frequency of ${6.2}_{-1.6}^{+2.8}$% for giant planets in orbits from 3 to 7 au...Our results are consistent with the literature, i.e., that Jupiter-like planets in Jupiter-like orbits are relatively uncommon""

What do you think?

[Res Ipsa]

The odds that intelligent life occurred in our solar system, regardless of how you choose to characterize it, are 1-1.

That's not what I am saying. I am simply wondering why we live in an unusual solar system. Is it because
A) We are very lucky to have an unusual solar system.
OR
B) Life is not possible in the vast majority of solar systems, so life here is just the result of a selection effect.

But you aren't simply wondering why we live in an unusual solar system. Your OP is about the probability of life in the universe. The major step you skip is connecting certain attributes of our solar system with the effect those attributes have on the probability of life forming.

The degree to which our solar system is "unusual" is purely a function of the number of different attributes you choose to consider.

Do the same exercise with people. Look at enough attributes, and the odds of you being you are 1 in 8 billion. Wow, you must be really lucky. Except that using the same process, everyone is unique. So, the odds that you are unique are 1 in 1. You're only as lucky as everyone else, which doesn't seem lucky at all.

We don't have any evidence of how the presence of a Jupiter analog affects the probability of life forming on a planet within the solar system. We don't know how the absence of a super earth among the inner planets affects the probability of life forming on a planet within the solar system. All solar systems have samenesses and differences. But unless you know which samenesses and differences matter when it comes to the formation of life, the exercise you are doing is meaningless when it comes to the probability of other intelligent life in the universe.

Given the number of stars in the universe, the presence of life on Earth is inconsistent with that "possibility." We have no reason to believe that.

Sean Carroll said, "Life could just be rare. Probability of life starting could be 10^-100 per planet. We just don’t know ". If the probability of life is 10^-100, then alien life in our universe would be effectively impossible.

However, string theory allows for 10^272,000 universes. The number of stars in our universe is nothing compared to 10^272,000. There could be an infinite number of universes. So, it's possible we are alone in our universe, but alien life existing in other universes.

"We just don't know" means exactly that. But the fact that we exist is evidence that the odds are not so long as to make our own existence virtually impossible. We also have no evidence that string theory represents reality. It is an untestable theory. Like God.

It suggests that our sun could also go through periods of variability similar to those of other solar-type stars.

That's possible, but wouldn't those periods be very unusual?

What evidence do you have for that? For what percentage of the life of the comparison stars do we have observations?

So, the presence of an outer gas giant in a solar system doesn't hinder the formation of inner super earths, with the lower bounds of super earths being planets of essentially the same mass or radius as Earth's. The paper says absolutely nothing about the likelihood of intelligent life forming in other solar systems.

That's not the point I made there. I am simply trying to demonstrate that our solar system is unusual. It's probably a good thing that Mars or Venus are not a Mini-Neptune.

It's probably a good thing that they aren't lots of things. That says nothing about the probability of other life in the universe. As an aside, you went on to multiply the probabilities even though the paper itself concludes that the two features are not independent.

So, were going to play the lift a single sentence out of a paper game and treat it as if it's established fact. I'd hoped you'd learned by now how unreliable that is if you are interested in drawing supported conclusions. So, the data comes from the Anglo-Australian Planet Search. What is that? Well, it's a project to search the brightest stars visible from the southern hemisphere to look for planets.

Here's what the paper says, "From a sample of 202 solar-type stars, and correcting for imperfect detectability on a star-by-star basis, we derive a frequency of ${6.2}_{-1.6}^{+2.8}$% for giant planets in orbits from 3 to 7 au...Our results are consistent with the literature, i.e., that Jupiter-like planets in Jupiter-like orbits are relatively uncommon".
https://iopscience.iop.org/article/10.3 ... X/819/1/28

The majority of stars are red dwarfs, solar-type stars are brighter than red dwarfs.

I know the 202 sample is small, but I doubt the Astrophysical Journal would accept papers that have useless samples.

Now you're going to lift out a piece of the background context I provided for the study and respond to that piece?

You're grasping at straws. The brightness of a star as viewed from earth is a function of what? What did you leave out?

I'm not criticizing the paper. The sample size is fine for what the paper actually does: testing a simulation against other methods of estimating Jupiter analogs. It's not fine for what you try to do with it. It's literally a handful out of a trillion trillion stars.

[doubtingthomas]

But the fact that we exist is evidence that the odds are not so long as to make our own existence virtually impossible.

Do you understand how small 10^-100 really is? A 10^-100 probability makes the existence of alien life virtually impossible in the observable universe. If the odds of life are 10^-100, then we would need something much bigger than the observable universe for alien life to form. A multiverse would explain extremely improbable formations, including our existence.

Sean Carroll said, "We can’t conclude that there must be intelligent life elsewhere just because the universe is big. It’s perfectly possible we’re the only ones here, with all the responsibility that implies."

He argued, "My guess is that there is not intelligent life in the observable universe other than us. Simply on the basis of the fact that the likely number of other intelligent species in the observable universe, there's two likely numbers, zero or billions, and if there have been billions, you would have noticed already"

But unless you know which samenesses and differences matter when it comes to the formation of life

It's very hard to prove what matters for the formation of life. It's much easier to prove that our solar system is unique. If the solar system is "a cosmic oddity", then that would be a strong hint that life is extremely rare in our observable universe.

The degree to which our solar system is "unusual" is purely a function of the number of different attributes you choose to consider. Do the same exercise with people. Look at enough attributes, and the odds of you being you are 1 in 8 billion...All solar systems have samenesses and differences

I am not claiming that all solar systems should be exactly the same, here's what the literature says

"Is our solar system a cosmic oddity? Evidence from exoplanets says yes"
https://www.newscientist.com/article/mg ... -says-yes/

What evidence do you have for that?

Let me ask, if the Sun is usually loud like most Sun-like stars, then why is the Sun not loud right now? The Sun hasn't been loud for the last 9,000 years according to the researchers. "Solar activity can be reconstructed over longer periods, up to 9000 years, from cosmogenic isotopes" https://arxiv.org/pdf/2005.01401.pdf What are the odds that the Sun is unusually quiet right now?

Now let's flip things. If it's common for sun-like stars to be "less active" or quiet, then why are the majority of Sun-like stars (similar mass, sizes, and rotation periods) very loud?

Here's how the researchers selected their sample

To compare solar photometric variability with other stars, we focus on Kepler observations of main-sequence stars with near-solar fundamental parameters and rotation periods. The stellar fundamental parameters we consider are the effective temperature Teff, surface gravity log g, and metallicity [F e/H] (18, 19). We adopt a parameter catalog (19) that is based on Kepler data release 25 (DR25). Rotation period measurements are available for thousands of stars observed during the Kepler mission (20,21). We adopt a catalog of 34,030 stars with determined rotational periods, and 99,000 stars for which no rotation periods were detected [ (21), their tables 1 and 2]. We refer to these as the ”periodic” and the ”non-periodic” samples. From both samples we select stars with effective temperatures in the range 5500–6000 K (the value for the Sun (subscript ) is Teff, = 5780 K) and surface gravities log g > 4.2 (Sun: log g = 4.44) to focus on solar-like main-sequence stars. The surface gravity cut removes evolved stars, which are inactive, so may have diluted the variability of solar-like stars found in previous analyses (21). For the periodic sample, we select rotation periods in the range 20–30 days (Sun: Prot, = 24.47 days sidereal rotation period)

https://arxiv.org/pdf/2005.01401.pdf