Do you think ET life exists elsewhere?

[Buzz Bloom]

Our best current theory puts the universe at about 96 billion light years acorss.

Hi Dave:

I may be mistaken, but I believe you have confused "universe" with "observable universe". Also, I understand that some older models had the universe expanding with the possibility that the expansion might stop and be followed by contraction. Those models corresponded to a finite universe. However, I understand that the acceleration of the expansion can only occur in GR cosmological models that are infinite.

Regards,
Buzz

 

[DaveC426913]

Fair enough. Still, the Big Bang Theory - our best understanding of creation - constrains the size of the universe.

 

[phinds]

2. I also understand the BEST current astronomical information fits a model in which the universe is expanding and the expansion is accelerating. Furthermore, this model requires that the universe must be infinite.

No, it has no such requirement. Still, as @PeterDonis often points out, our best model does suggest that the universe is infinite in extent but I don't believe even he states it as a known fact, just the most likely model.

 

[Buzz Bloom]

Fair enough. Still, the Big Bang Theory - our best understanding of creation - constrains the size of the universe.

Hi Dave:

Again this is (almost) true about the "observable universe, not the "universe. Also, with respect to the observable universe, out best cosmological models do not constrained it to any particular finite size. It's finite size continues to accelerate indefinitely at a rate that approaches exponential growth.

Regards,
Buzz

 

[DaveC426913]

... our best model does suggest that the universe is infinite in extent...

It seems I may have to go back and hit the books.

 

[phinds]

It seems I may have to go back and hit the books.

Do a search for Peter Donis' posts regarding this. He has mentioned it several times.

 

[DaveC426913]

Again this is (almost) true about the "observable universe, not the "universe.

I guess I'm a little confused as to what you're talking about.

You did say, in post 49 (point 2), "the universe is expanding". So, do you mean the universe - being infinite - is, at the same time, expanding?

 

[Buzz Bloom]

@PeterDonis often points out, our best model does suggest that the universe is infinite in extent but I don't believe even he states it as a known fact, just the most likely model.

Hi phinds:

As I understand from reading the @PeterDonis mathematical presentations about the current best model, his description of the best fit model does not specify the universe as being infinite or finite. However, I believe this is because the issue is not relevant to the math he was explaining.

I am getting the impression that the particular phrase I used in #47 may have suggested to some readers that I intended it to imply the current best model is the final model for all future time to explain the large scale cosmology. However, I think #49 makes it as clear as I can that I do not believe this, and did not intend that interpretation. However, I have edited #47 to improve understanding.

Regards,
Buzz

 

[Buzz Bloom]

You did say, in post 49 (point 2), "the universe is expanding". So, do you mean the universe - being infinite - is, at the same time, expanding?

Hi Dave:

I have edited my original post to help clarify my intended thoughts. Although I am far from being an expert, I would now phrase what you have in italics as follows to avoid further misunderstanding. To clarify, it is the scale factor of the universe that is expanding and accelerating. The variable "a" in the Friedman equation represents the scale factor.

The universe is expanding, and the expansion is accelerating. The Friedman equation (see below) together with the current best fit values of the four Ω coefficients corresponding to the current best model, implies that there is a relatively high degree of confidence that the best value of Ω_k is sufficiently negative that it specifies an open infinite universe, that is, either a hyperbolic universe or a flat universe. However, the probability is pretty small that Ω_k may at some later time, after new astronomical data is available, be part of a new best model with a positive value of Ω_k implying a closed finite universe.​

Regards,
Buzz

 

[nitsuj]

I guess I'm a little confused as to what you're talking about.

You did say, in post 49 (point 2), "the universe is expanding". So, do you mean the universe - being infinite - is, at the same time, expanding?

The universe is expanding at rates greater than c, the issue of observing it to being infinite. such a thing can only be modeled.

imo from a physics perspective if something is outside our "causal structure" what's the significance?

 

[phinds]

The universe is expanding at rates greater than c,

That is not really a correct way of stating it. Yes, things over a certain distance from each other are receding from each other at recession velocities greater than c, but that is not the "speed of recession of the universe" as you seem to believe. The universal expansion should be expressed as about (67 Km/Sec)/Parsec. This properly captures the fact that things farther apart are receding from each other faster than things closer together.

EDIT: Hm ... didn't remember the exact rate so looked it up and I think what I stated is incorrect. It should be (67 Km/Sec)/(10E6 Parsecs), or more concisely, (67 Km/Sec)/(MParsec)

 

[OCR]

Do you think ET life exists elsewhere?

Eh... ?

 

[phinds]

Eh... ?

View attachment 215729​

Hey, don't blame me for sidetracking the thread. I was just responding to a post.

 

[DaveC426913]

Eh... ?

Buzz Bloom's post #47 opened the door to discussions about the extent of the universe as it might pertain to the probability of life.

 

[DS2C]

Voted "probably". I can't prove or disprove it, but as Carl Sagan said- "If it's just us, seems like an awful waste of space." Pretty much sums it up for me.

 

[NFuller]

I believe evolving life on Earth has a possibility of $\frac {1} {10^{22}}$

How did you arrive at this number?

I find it hard to believe that the probability of life evolving on Earth is as low as you stated considering how rapidly life showed up after the crust solidified.

 

[Arman777]

How did you arrive at this number?

I find it hard to believe that the probability of life evolving on Earth is as low as you stated considering how rapidly life showed up after the crust solidified.

Observable universe have roughly $10^{11}$ galaxy and each galaxy have roughly $10^{11}$ star. So I just multiplied them and I assumed that, we are the only one in the universe since.So there's $10^{22}$ star and our solar system has the only one that contains life.So in some sense it makes sense to me (even you can multiply that number with average planet number on every star). The probabilty is referring to us that our probabilty of existence is $\frac {1} {10^{22}}$.If there's another life it will have same probabilty. My logic might be wrong and probably wrong.But even its wrong it must be really low which I am sure of it.

 

[russ_watters]

Observable universe have roughly $10^{11}$ galaxy and each galaxy have roughly $10^{11}$ star. So I just multiplied them and I assumed that, we are the only one in the universe since.So there's $10^{22}$ star and our solar system has the only one that contains life.So in some sense it makes sense to me (even you can multiply that number with average planet number on every star). The probabilty is referring to us that our probabilty of existence is $\frac {1} {10^{22}}$.If there's another life it will have same probabilty. My logic might be wrong and probably wrong.But even its wrong it must be really low which I am sure of it.

That's the known per star probability, but the OP asks about the universe. The probability of one planet with life in the universe is 100% 1/1. If a second is found it is 2/2=200%

 

[nitsuj]

That is not really a correct way of stating it. Yes, things over a certain distance from each other are receding from each other at recession velocities greater than c, but that is not the "speed of recession of the universe" as you seem to believe. The universal expansion should be expressed as about (67 Km/Sec)/Parsec. This properly captures the fact that things farther apart are receding from each other faster than things closer together.

EDIT: Hm ... didn't remember the exact rate so looked it up and I think what I stated is incorrect. It should be (67 Km/Sec)/(10E6 Parsecs), or more concisely, (67 Km/Sec)/(MParsec)

lol none of that detracts from or adds to my point.

 

[Arman777]

2/2=200%

I didnt understand this part. My previous approach was wrong. Let's suppose something similar. Image a universe has 12 planets and we can't see 9 of them. We are living one them and we know that other 2 doesn't contain any life.Whats the probability of others containing life ?

It has nothing to do with respect to the planet number. Its most likely about the circumtances that can cause to form a live. Which is tempature,water and other elements etc. And there's another thing which If you even satisfy these conditions life just doesn't pop up.

In our case we don't know these conditions and its hard to calculate the probability of it.But I believe that It would be really really low.

Probably of live=1 / (The all possiblities that can cause life)

 

[Buzz Bloom]

No, it has no such requirement. Still, as @PeterDonis often points out, our best model does suggest that the universe is infinite in extent but I don't believe even he states it as a known fact, just the most likely model.

Here is a quote from a PeterDonis post.

https://www.physicsforums.com/threads/infinite-versus-finite-space.924230/page-2#post-5838552
To be clear, the spatially infinite universe is the best fit to the data we have. But given the unavoidable uncertainty in our measurements, it is still possible (though unlikely) that the universe is spatially finite.​

I think that this saying exactly what I intended. I get that you find any unqualified statement about a scientific fact to be misleading. I do not disagree with this, but I think the possibility of someone who understands that almost all scientific facts are tentative would not be misled.

Regards,
Buzz

 

[russ_watters]

I didnt understand this part.

Sorry, that was a typo; should have been 2/1=200%

 

[BillTre]

Image a universe has 12 planets and we can't see 9 of them. We are living one them and we know that other 2 doesn't contain any life.Whats the probability of others containing life ?

The problem is that we know that our planet houses very a very complex and productive ecology of easily observable life processes.
Many admit that life on other planets could be much more sparse and cryptic than what we experience here. Making it more difficult to observe.
We don't know any other celestial bodies in anything approaching the depth of what we know of Earth conditions.

I would argue that it is difficult to even rule out life on any other celestial body (mostly planets and moons) because in no cases (except possibly the moon) are enough known about conditions on other planets to reasonably rule out life being hidden away somewhere out of our observational view.
Meanwhile we know several places where there are indications of conditions where complex chemical processes might be able to cling to life, in our solar system:

• the moons with liquid water
• Mars (methane bursts, water present, deep holes what different atmospheric conditions (such as Hellas Basin))
• Mercury (has water, has a perpetual zone between it illuminated and dark sides with intermediate conditions)
• Moons with liquid organics rather than water
• Gas giant planets with unknown chemistries buried deep within them

To me at least, none of these have been ruled out by any observations we have made. They could too easily be false negatives!
Therefore, I prefer @russ_watters's assessment of a 1/1 scoring our current knowledge of life's existence.

 

[PeroK]

I didnt understand this part. My previous approach was wrong. Let's suppose something similar. Image a universe has 12 planets and we can't see 9 of them. We are living one them and we know that other 2 doesn't contain any life.Whats the probability of others containing life ?

It has nothing to do with respect to the planet number. Its most likely about the circumtances that can cause to form a live. Which is tempature,water and other elements etc. And there's another thing which If you even satisfy these conditions life just doesn't pop up.

In our case we don't know these conditions and its hard to calculate the probability of it.But I believe that It would be really really low.

Probably of live=1 / (The all possiblities that can cause life)

There's no answer to the question, but one answer I think can be ruled out (from the information we have available):

"That it's impossible or nearly impossible for life to be anywhere else in the universe."

That, at this stage, is an invalid answer; not based on a rational analysis of the data.

It may turn out that there is no life, but I can't see the evidence to rule it out.

In any case, the evidence of our solar system suggests that conditions for life may be quite common. You cannot say definitely how common it is. But, to look at our solar system and shake your head sadly and say - with almost certainty - nothing like this can possibly exist anywhere else in the universe is not logical or rational. Our solar system may be unique, but you cannot assert with near certainty that it is unique.

It seems to me also that breaking it down into the thousands of things that may or may not have been essential for life is likewise false logic. We don't know that if one of these didn't happen, then life definitely wouldn't have evolved on Earth. We can look at the big picture and see that life did evolve. It may have evolved without all those "lucky" chances. We don't really know how difficult it is for life to evolve, so we cannot rule out its being common across the billions of stars and billions of galaxies.

 

[nitsuj]

I wonder about plants, surely there is a planet out there with plants that absorb much greater energy than here. What is a 90 watt plant capable of! ATTACK of the planet plants!

 

[NFuller]

Its most likely about the circumtances that can cause to form a live. Which is tempature,water and other elements etc. And there's another thing which If you even satisfy these conditions life just doesn't pop up.

Considering Earth as the only example we have, life actually did just seem to "pop up" once conditions became favorable. Liquid water first appeared on Earth about 4.4 billion years ago. The first cells appeared about 4.3 billion years ago: a mere 100 million years after liquid water appeared. It might not have even taken that long, it's possible that new evidence will be found which will push the starting date for life even earlier.

The fact that life seems to be so readily formed, at least on Earth, suggests that the probability to form life may be rather large and that the conditions sufficient for abiogenesis may not be too particular.

 

[Arman777]

Considering Earth as the only example we have, life actually did just seem to "pop up" once conditions became favorable.

I agree. Thats also why its hard for me to believe an ET life form.There are just theories that trying to explain the formation of live on earth.

The fact that life seems to be so readily formed, at least on Earth, suggests that the probability to form life may be rather large and that the conditions sufficient for abiogenesis may not be too particular.

I like PeroK's post (#74) in this sense. In the vote section I voted unlikely, there could be life just I don't believe in that much.

 

[DaveC426913]

I agree. Thats also why its hard for me to believe an ET life form.There are just theories that trying to explain the formation of live on earth.

It should lead you to believe the opposite.

Having only one sample does not in-and-of-itself suggest ET life is rare.

In fact, in the one instance where life-as-we-know has popped up, it seems to have defied the odds of life not being common.

It seems that, almost the moment conditions became suitable, life took hold.

 

[Dr. Courtney]

It seems that, almost the moment conditions became suitable, life took hold.

It seems your moments are a bit longer than my moments. There are various competing hypotheses regarding how chemical evolution gave rise to abiogenesis, but time scales seem to range from 1 million to 100 million years. I'm not sure how one can assign a span to the process before one of these hypotheses gathers enough evidence to be a real theory.

 

[DaveC426913]

... time scales seem to range from 1 million to 100 million years. I'm not sure how one can assign a span to the process before one of these hypotheses gathers enough evidence to be a real theory.

Even the most pessimistic of those is fairly quick in geologic time.
The Earth's surface was molten for quite some time, and even once it had cooled, it suffered 100 million years of bombardment, and still had to wait for comets to come and deposit water.

That greatly constrains the earliest time before conditions were suitable at all. And that leaves not a lot of time left in there for a suitably conditioned Earth to be lifeless before life came along.

And even that's based on the fossils that have survived for 5 billion years. It doesn't count anything that might have been around before, whose fossils have not been preserved.

 

[russ_watters]

It seems your moments are a bit longer than my moments. There are various competing hypotheses regarding how chemical evolution gave rise to abiogenesis, but time scales seem to range from 1 million to 100 million years. I'm not sure how one can assign a span to the process before one of these hypotheses gathers enough evidence to be a real theory.

Ok, so how long are your geological "moments"? A million years after water first became liquid is about 4 billion years ago. A hundred million years after water first became liquid is also about 4 billion years ago. Why quibble about single digit percentages?; 1 vs 99 million years out of 4.4 billion is pretty fast either way. A pretty small window.

 

[Dr. Courtney]

Ok, so how long are your geological "moments"?

Ok, so we're talking about geological moments. Please correct me if I am wrong, but I don't recall the adjective "geological" as a modifier for the use of the word "moment" that I disagreed with.

 

[DaveC426913]

Ok, so we're talking about geological moments. Please correct me if I am wrong, but I don't recall the adjective "geological" as a modifier for the use of the word "moment" that I disagreed with.

That would be implicit in the context of the thread.

Did you honestly think I meant "less than a few seconds"?

 

[Dr. Courtney]

That would be implicit in the context of the thread.

Did you honestly think I meant "less than a few seconds"?

It's not about your intent, but about the ambiguity and various ways it could be interpreted by the broad readership of Physics Forums, some of whom may not yet be familiar with the concept and magnitudes of geologic time. The concept of geologic time had not been mentioned a single time in this discussion when the statement was made, "It seems that, almost the moment conditions became suitable, life took hold."

Good science and good education practices are mindful of the full audience and are careful not to assume unstated definitions (a relative moment on the geologic time scale) rather than definitions in more common use (a normal moment in human experience.) A statement that may make perfect sense in an astrobiology journal may leave many PF readers confused.

 

[DaveC426913]

I think you're being pedantic. The time frame is implicit in the context of the discussion - the start of life on Earth, 4.5 Gy ago.
Why would you assume people will think "seconds"?
Anyway, we've wasted more time arguing it than necessary.

 

[russ_watters]

It's not about your intent, but about the ambiguity and various ways it could be interpreted by the broad readership of Physics Forums, some of whom may not yet be familiar with the concept and magnitudes of geologic time. The concept of geologic time had not been mentioned a single time in this discussion when the statement was made, "It seems that, almost the moment conditions became suitable, life took hold."

Good science and good education practices are mindful of the full audience and are careful not to assume unstated definitions (a relative moment on the geologic time scale) rather than definitions in more common use (a normal moment in human experience.) A statement that may make perfect sense in an astrobiology journal may leave many PF readers confused.

You are being pedantic, for really no good reason. The timeframe itself was given - numerically - in the discussion you responded to and you appear to have known it yourself! So it should have been clear that's what the labels were referring to. Either way: since you now seem to understand, does that change your view on the issue being discussed? You agree that in terms of the time available for life to occur, it occurred in a small fraction of that time. Right?

 

[Dr. Courtney]

You are being pedantic, for really no good reason. The timeframe itself was given - numerically - in the discussion you responded to and you appear to have known it yourself! So it should have been clear that's what the labels were referring to. Either way: since you now seem to understand, does that change your view on the issue being discussed? You agree that in terms of the time available for life to occur, it occurred in a small fraction of that time. Right?

100 million years is about 1/45 of the geologic time scale, probably more comparable to a year than a moment in typical human experience.

1 million years is about 1/4500 of the geologic time scale, probably more comparable to 3 days or so than a moment in typical human experience.

Even if it were clear that a geologic time scale is being discussed, 1-100 million years seems like a lot more than a geologic "moment" when scaling to typical human experience.

If you ask someone for something and their reply is "I'll be with you in a moment" do you feel they have kept their word if their delay is between 3 days and 1 year?

 

[russ_watters]

100 million years is about 1/45 of the geologic time scale, probably more comparable to a year than a moment in typical human experience.

1 million years is about 1/4500 of the geologic time scale, probably more comparable to 3 days or so than a moment in typical human experience.

Even if it were clear that a geologic time scale is being discussed, 1-100 million years seems like a lot more than a geologic "moment" when scaling to typical human experience.

If you ask someone for something and their reply is "I'll be with you in a moment" do you feel they have kept their word if their delay is between 3 days and 1 year?

So what you are saying is you have no intention of discussing the topic the rest of us are discussing and would rather just keep arguing over what colloquial label to apply?

 

[DaveC426913]

If you have a counter statement to make that is relevant to the discussion at-hand about how long it took life to form, feel free to make it.
I'd suggest that we save the discussion about definitions of 'moment' for a different thread in a different forum.
The meaning is clear from the context.

 

[berkeman]

Thread closed for Moderation...

 

[fresh_42]

About the last dozen of posts here seem to be an argument on how "moment" in the various timescales may be interpreted. So this thread has run its course. Furthermore the topic itself is highly speculative and opinions are driven by a vast number of additional assumptions, from religious over probabilistic to detection related ones. This isn't by no means an allegation, but since we don't even know, whether other life forms exist in our own solar system nor how they might look like, a basis to seriously debate upon seems not to be given.

Thread remains closed.