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View Full Version : Who says life has to meet Earth's requirements?



Zap
2003-Feb-17, 02:51 AM
http://www.space.com/scienceastronomy/astrobio_weird_030214.html

Who says you need water to have life? Who says you need CO2? Maybe we will find life thriving on other chemicals that Earth life would commonly find disgusting.

Man the possibilities are endless...but see my question is how will we go about searching for extraterrestial life in other places? Even in the solar system its going to be a hard costly task.

johnwitts
2003-Feb-17, 04:06 AM
It's another example of Earthcentric thinking. Look at the latest WMAP survey. It puts us squarely at the centre of the universe. What are the chances of that?

JS Princeton
2003-Feb-17, 04:22 AM
I hope you're being tongue-and-cheek when you say that WMAP puts us at the center of the universe.

But more than that, "Earthcentrism" is really the best science can do at this point from an observational perspective in astrobiology. Sure, we can theorize till we're blue in the face about weird chemistries and lifeforms made of buckyballs, but until they're observed we're going to have no idea how these "out of the box" creatures will appear. We might consider the philosophical questions of "what is life?" that arise from thinking out-of-the-box, but coming up with specific biochemistries, base solvents, and active molecular structures runs the risk of going on wild goose chases.

However, sometimes wild goose chases are useful. If you are interested in the area and can get funding, I'd say go for it. However, for now we stick with the one data point we have (even though it's statistically unsound) and deal with what we know and work from there. After all, we hardly have the last word written about life yet on this planet... we keep finding stranger and stranger beasts in any case. In fact, we can't even begin to identify one tenth of one percent of the different species on Earth; we have found life in the strangest places. When things that we know are related to us are so weird, how are we to begin to think about life that is not "like us"?

johnwitts
2003-Feb-17, 04:26 AM
I was semi serious with my comment. Everywhere we look the 'edge of the universe' seems to be the same distance away. How can this be? It has always puzzled me. Maybe my lack of understanding is showing, but if the universe is 'flat' then I don't understand how the edges can be a constant distance away no matter which direction we look. Hmm...

xriso
2003-Feb-17, 05:51 AM
On 2003-02-16 23:26, johnwitts wrote:
I was semi serious with my comment. Everywhere we look the 'edge of the universe' seems to be the same distance away. How can this be? It has always puzzled me. Maybe my lack of understanding is showing, but if the universe is 'flat' then I don't understand how the edges can be a constant distance away no matter which direction we look. Hmm...


The "edge of the universe" is really just the visible edge.



It's kind of like the way the horizon is always the same distance away from you, no matter where you are.

xriso
2003-Feb-17, 05:53 AM
So, has anybody ever actually come up with a feasible alternative to "carbon and water" life?

kilopi
2003-Feb-17, 10:18 AM
On 2003-02-17 00:53, xriso wrote:
So, has anybody ever actually come up with a feasible alternative to "carbon and water" life?

Folks speculate all the time. From the point of view of the maximum number of possibilities--to afford the possibility of some sort of evolution--the carbon bond is probably the best bet. Silicon would fit in there, as its atomic number is eight more than carbon, but not quite as well--so there has been a great amount of speculation in that direction.

Mainframes
2003-Feb-17, 11:31 AM
You'd have to look a long time to find anything that is as good as water for sustaining a lifeform.

Excellent solvent
Good heat capacity
Formed as a by-product of numerous chemical reactions
Stable
Simple Molecule

etc. etc.

Sleepy
2003-Feb-17, 01:34 PM
Two books with differing ideas:

Evolving the Alien by Jack Cohen and Ian Stewart.

Here Be Dragons by David Koerner and Simon LeVay

<font size=-1>[ This Message was edited by: Sleepy on 2003-02-17 08:38 ]</font>

JS Princeton
2003-Feb-17, 03:13 PM
xriso gave a good explanation for the "edge of the universe" problem. It is basically a consequence of the universe being finite in time. As the universe need not be finite in space (at this point in history), there is no reason to accept that we have to be at the spatial middle.

Zap
2003-Feb-17, 03:21 PM
Why do we always have to be in the middle?? I don't see whats so difficult about accepting the idea that the Earth is NOT in the center of the universe. IF the universe is infinite in space, then of course there is no possible way to be in the middle anyways.

kilopi
2003-Feb-17, 03:32 PM
On 2003-02-17 10:21, Zap wrote:
IF the universe is infinite in space, then of course there is no possible way to be in the middle anyways.

Wouldn't that also mean that no matter how far we looked, we'd be in the middle of how far we can look?

Zap
2003-Feb-17, 03:36 PM
On 2003-02-17 10:32, kilopi wrote:


On 2003-02-17 10:21, Zap wrote:
IF the universe is infinite in space, then of course there is no possible way to be in the middle anyways.

Wouldn't that also mean that no matter how far we looked, we'd be in the middle of how far we can look?


Yeah true. But we still wouldn't be in the "middle." This would be the case with every celestial body.

kilopi
2003-Feb-17, 03:39 PM
I'm assuming that you meant that every other celestial body would not be at the middle of how far we can look, but at the middle of how far they (whoever they are) can look, right? Right now though we don't even know if they exist.

Zap
2003-Feb-17, 03:42 PM
On 2003-02-17 10:39, kilopi wrote:
I'm assuming that you meant that every other celestial body would not be at the middle of how far we can look, but at the middle of how far they (whoever they are) can look, right? Right now though we don't even know if they exist.


Right. And whether or not "they" exist is a different matter altogether...

Basically my point was that if the universe is infinite in space, there technically wouldn't be a center. Not around Earth, not anywhere.

JS Princeton
2003-Feb-17, 03:44 PM
The locations exist, of that we're certain. As to whether someone is sitting there looking, well... it's a question for the ages.

johnwitts
2003-Feb-17, 03:56 PM
So, if we can't see the actual edge, how do we know how old it is?

kilopi
2003-Feb-17, 04:02 PM
Extrapolation. If we know how fast they're going and how far they are, we can infer when they were together.

Zap
2003-Feb-17, 04:03 PM
On 2003-02-17 10:56, johnwitts wrote:
So, if we can't see the actual edge, how do we know how old it is?


Measurements of the amount of "stuff" (or matter) in the visible universe over a period of time helps get somewhat of a time scale for its age. Also, remember the further we see, the further back in time it is. Monitoring the motions of galaxies and black holes also helps. For more information on this subject here is a recent article released about mapping the Big Bang.
http://skyandtelescope.com/news/current/article_877_1.asp

_________________
If you didn't like the opinions expressed in this post, get over it!

<font size=-1>[ This Message was edited by: Zap on 2003-02-17 11:04 ]</font>

johnwitts
2003-Feb-17, 07:41 PM
So, how far back can we see?

Moose
2003-Feb-17, 08:04 PM
On 2003-02-17 10:42, Zap wrote:
Basically my point was that if the universe is infinite in space, there technically wouldn't be a center. Not around Earth, not anywhere.


Fair enough.

So.

Where would you correctly place the Earth on an accurate projection then?

Hint: We don't know where we are in relation to the "edge", even assuming there is one. Until we can define a "fixed" edge, an Earth-centric projection gives us the most bang for the buck. (Pun not intended, but gleefully accepted.)

JS Princeton
2003-Feb-17, 08:16 PM
On 2003-02-17 14:41, johnwitts wrote:
So, how far back can we see?


Until the time of last scatter (the CMB surface) a few hundred thousand years after the Big Bang.

DaveC
2003-Feb-17, 09:21 PM
On 2003-02-17 14:41, johnwitts wrote:
So, how far back can we see?


Something like 13 billion years. If you have really bad eyesight, you may only be able to see back about 8 minutes when you look at the sun - which will give you even worse eyesight! /phpBB/images/smiles/icon_smile.gif

cable
2003-Feb-17, 09:27 PM
On 2003-02-16 23:22, JS Princeton wrote:
..........
But more than that, "Earthcentrism" is really the best science can do at this point from an observational perspective in astrobiology ......

xtrapolating what we see on earth to the whole universe may be somewhat pretentious.

u r assuming that gravity as seen on earth is the same everywhere. it could be valid only for our galaxy.

same could be said about speed of light, or DNA ....

too much extrapolation .

cable
2003-Feb-17, 09:32 PM
On 2003-02-17 00:51, xriso wrote:
The "edge of the universe" is really just the visible edge.



It's kind of like the way the horizon is always the same distance away from you, no matter where you are.

FINE.
if u can't see beneath the horizon, ie. a big part of the universe remains invisible, how could u estimate the mass of the whole universe ??

JS Princeton
2003-Feb-17, 09:39 PM
On 2003-02-17 16:27, cable wrote:


On 2003-02-16 23:22, JS Princeton wrote:
..........
But more than that, "Earthcentrism" is really the best science can do at this point from an observational perspective in astrobiology ......

xtrapolating what we see on earth to the whole universe may be somewhat pretentious.

u r assuming that gravity as seen on earth is the same everywhere. it could be valid only for our galaxy.

same could be said about speed of light, or DNA ....

too much extrapolation .





You can say that DNA might not be the base molecule for life, but we have observational limits on how gravity or the speed of light changes. Basically, they are the same everywhere in the observable universe.

JS Princeton
2003-Feb-17, 09:40 PM
On 2003-02-17 16:32, cable wrote:


On 2003-02-17 00:51, xriso wrote:
The "edge of the universe" is really just the visible edge.



It's kind of like the way the horizon is always the same distance away from you, no matter where you are.

FINE.
if u can't see beneath the horizon, ie. a big part of the universe remains invisible, how could u estimate the mass of the whole universe ??


No one says we do. All we do is measure a density which from the size of the universe (determined by multiplying the age of the universe by the speed of light) will give us a mass of the observable universe.

Zathras
2003-Feb-17, 09:47 PM
On 2003-02-17 16:40, JS Princeton wrote:
. . .
No one says we do. All we do is measure a density which from the size of the universe (determined by multiplying the age of the universe by the speed of light) will give us a mass of the observable universe.


I don't think this is correct. The expansion of the universe has not been going on at the speed of light. If the universe started out with a small, finite size, then your calculation for the size of the observed universe would turn out to be greater than the size of the actual universe.

JS Princeton
2003-Feb-17, 10:05 PM
Actually, we inflationary theory predicts the expansion of the universe to be faster than the speed of light for that epoch. This is why the technique basically works: it defines a particle horizon (an observational limit). It is not a "fiducial" size of the universe (there are other horizons for that) but rather it is a size of the universe that we can ever hope to observe. Therefore it is the size of the universe that should determine all the observational quantities (assuming that the Cosmological Principle holds on much larger scales).

As we are currently in an accelerating expansion phase, it looks like we will actually begin to see less and less of the universe's objects too. We'll always be able to look back to the beginning of time, but we woon't always be able to see things that are "right next door" if the accelerating universe continues.

johnwitts
2003-Feb-17, 10:55 PM
That just doesn't make sense. We can see 13 billion light years away, therefore 13 billion years ago. That makes the universe 26 billion light years across. Someone is making stuff up. It doesn't make sense. If it's a long way away, it's a long time ago. If it's a long time ago, everything was much closer together. Are you saying that 13 billion years ago the universe was 26 billion light years across? Hardly small.

DaveC
2003-Feb-17, 11:21 PM
On 2003-02-17 17:55, johnwitts wrote:
That just doesn't make sense. We can see 13 billion light years away, therefore 13 billion years ago. That makes the universe 26 billion light years across. Someone is making stuff up. It doesn't make sense. If it's a long way away, it's a long time ago. If it's a long time ago, everything was much closer together. Are you saying that 13 billion years ago the universe was 26 billion light years across? Hardly small.


OK, I just made that stuff up to see if you were paying attention. /phpBB/images/smiles/icon_smile.gif

If the model was simply a bunch of stars and galaxies retreating from an explosion point at speeds ranging up to (almost) the speed of light, your conclusion would appear to make sense. But the space between the masses in the universe is expanding too - much faster than the movement of the matter "away from the site of the Big Bang" would suggest. Based on what we know, the big bang happend sometime around 13 to 14 billion years ago. All that stuff 13 billion light years away was together at a single point that existed everywhere in the universe. Clearer now?

(Anytime soon one of the real physicists here will weigh in with a real explanation.)

JS Princeton
2003-Feb-17, 11:23 PM
It does seem strange, doesn't it, john? The problem you are having is dealing with a "metric" that is expanding. This is something that cosmologists also have trouble with so they use "comoving" coordinates in order to avoid confusion. This basically means that you set up a new measurement system that allows you to measure distances and times without having to worry about the fact that everything is moving with respect to everything else (all raisin-bread-like).

Indeed, if you point 180 degrees apart from yourself to two points in the sky that are 13 billion lyrs away (say two different anisotropies in the CMB) you will be pointing to two objects that are 26 billion light years from each other. They are so far away they haven't had time to come into contact with each other. This "causality" effect is something that drives the theory of inflation in order to explain the continued homogeneity of the CMB. However, when we measure distances at 13 billion light years, the distances aren't the same! (Wha!?!? you say. Stay with me, sayas I.)

In order to measure distances of distant objects you need some sort of ruler. Now, you can use light as your ruler, and that will give you a conformal distance, but in that case you realize that these two objects you pointed to, if you were there, would not be able to see each other. Now that distance can be extapolated for late times or early times depending on the question you are asking. If you are at late times, you take your measurement at object A and wait until 13 billion years past. The universe expands and cools off, but you see a different part of the CMB surface than the guy back on Earth sees. If you measure the size of the universe 13 billion years ago, you will find it is extremely small no matter where you are in the universe. This is just due to the finite speed of light. You can't see anything (that's your particle horizon) beyond the age of the universe times the speed of light. That's the rule. You are not able to violate it. It sets the size of the universe.

Perhaps this is confusing because you're used to measuring things in a uniform and non-expanding world. If we had a world that was expanding, things would look very strange indeed, but you wouldn't think these comments to be at all odd. They are, actually, just artifacts of the way the universe evolves.

johnwitts
2003-Feb-18, 12:59 AM
Now my head really hurts. Let me get this straight. The Cosmic Microwave Background is actually like looking at the inside of a ping pong ball sized object, but once it was formed it got expanded outwards by a force that drags the entire contents of the universe along with it. It has become so stretched thin that the origional energy had been 'stretched' all the way down to the microwave region. Am I getting closer to even beginning to understand this? And this expansion force, is light exempt from it's effects? Duh, my brain was hurting before. Now it's falling off...

JS Princeton
2003-Feb-18, 01:08 AM
Well, you're getting close, but the CMB-surface was much, much, much bigger than a ping-pong. Actually, the observable radius at the surface of last scatter corresponds to about a time of 400,000 years or so. This means that the observable universe had a radius of 400,000 light years... or about the size of our galaxy today. However, since inflation had happened before then, the universe was actually larger than its observational (particle horizon) limit. So, more and more of the CMB surface becomes "visible" to more and more of the CMB surface (allowing causality).

Maybe it's time to take an asprin and head over to Ned Wright's cosmology pages. They're really quite good, I'd say.

SeanF
2003-Feb-18, 02:37 PM
On 2003-02-17 20:08, JS Princeton wrote:
...the observable universe had a radius of 400,000 light years... or about the size of our galaxy today.


Really? Last I remember learning, our galaxy has a radius of about 50,000 light-years. What'd I miss?

JS Princeton
2003-Feb-18, 02:48 PM
What you missed was simply order of magnitude. When we're talking about scaling the factors of 8 or so different between various measurements are trivial. When you consider that the universe right now has a radius of 13 BILLION light years, the difference between 400,000 and 50,000 is trivial indeed.

SeanF
2003-Feb-18, 02:57 PM
On 2003-02-18 09:48, JS Princeton wrote:
What you missed was simply order of magnitude. When we're talking about scaling the factors of 8 or so different between various measurements are trivial. When you consider that the universe right now has a radius of 13 BILLION light years, the difference between 400,000 and 50,000 is trivial indeed.


Oh, okay. I was just worried I'd missed some major discovery about the size of the Milky Way! /phpBB/images/smiles/icon_smile.gif

Thanatos
2005-Nov-29, 11:54 AM
What you missed was simply order of magnitude. When we're talking about scaling the factors of 8 or so different between various measurements are trivial. When you consider that the universe right now has a radius of 13 BILLION light years, the difference between 400,000 and 50,000 is trivial indeed.

I would have bit the bullet on that one, JS. I would not care to defend the proposition it is trivial whether or not the universe is 104 or 13 billion years old.

Jakenorrish
2005-Dec-07, 11:41 AM
In response to the original question, a very narrow minded person might say that life elsewhere has to meet the Earth's requirements. When I think of life in extra terrestrial locations or extra solar locations, I always try to keep an open mind when speculating.

Life in different locations on Earth will evolve to suit its location, conditions and subtle changes in these conditions, caused by air or water currents etc.

The same would be true of life wherever it may be, so if we do find it, it would only be the same as life on Earth if you find an identical location to Earth. I think that this particular circumstance can be ruled out. We may find similar locations which frankly will be very difficult to track down, but the life there will surely be quite different and also unique to its particular environment even if the differences are very subtle. That location's history and evolution will be different to ours even if conditions there when we arrive are similar to Earth's.

In fact we may find an entirely new type of organism and be trying to definine exactly what life is in future decades and centuries.

I think what I'm trying to say is keep a very open mind and expect the unexpected. I for one think as a scientist, that as soon as we set our expectations based on what we see on Earth, our discoveries outside of our planet always surprise us. We never expected any of what we've seen in the outer reaches of our solar system, I'm sure that when we do track down extra terrestrial life, it will be very far removed from what we thought we'd find.

Let's hope it isn't like the creature from the Alien films!

Doodler
2005-Dec-09, 04:23 AM
That just doesn't make sense. We can see 13 billion light years away, therefore 13 billion years ago. That makes the universe 26 billion light years across. Someone is making stuff up. It doesn't make sense. If it's a long way away, it's a long time ago. If it's a long time ago, everything was much closer together. Are you saying that 13 billion years ago the universe was 26 billion light years across? Hardly small.

Nah, the universe is something on the order of 76 billion light years across at the moment, based on projections of expansion since T=0 roughly.. We can only see 13.7 Gyrs out because that's all the time that's elapsed to allow light, radiation and everything else to traverse the distance between here and there.

Its uniform in dimension, because every point in the universe popped into existance simultaneously. Therefore, we'll always perceive the edge as a sphere centered on our location.

William_Thompson
2005-Dec-14, 01:10 AM
-- because without the sea there was no life on land on Earth for too long. That is why.