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Old 09-22-2017, 12:45 PM
 
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Originally Posted by Mark S. View Post
Yup. But the universe is also constantly expanding. So even if we could travel at the speed of light and spent 14 billion years doing so, by the time we reached our destination, the universe would have expanded by another 14 billion light years.
Good point. Taking into account such large scales, that would be true if the universe was NOT expanding. It would only work if the Universe was just spatial. But since Time is also a factor in the Universe, the "fabric" of space in the Universe is described as Space-Time, even though Time is not a spatial dimension. Even at the speed of light, you could not reach such distant destinations because the Universe continues to expand. To make matters even more complicated, the Universe (at large scales) is not only expanding, but it's expanding at an accelerated rate. The greater the distance there is between two objects, the faster the rate of expansion. In a nutshell, in terms of such extremely large distances, even at the speed of light, you couldn't get there from here because the Universe continues expanding at an accelerated rate.

We also have to take into account that everything in the Universe is in motion. When we see galaxies that are billions of light years away, we're not only seen them in terms of spatial distance, but we're also seeing them as they were billions of years ago. And since these galaxies would be in motion, we're seeing where they were billions of years ago, meaning those galaxies are no longer in the position that we see them to be in. They might not even exist anymore. Assuming those distant galaxies are still exist, anyone there looking at the Milky Way galaxy, would see our galaxy as it was billions of years ago. If Alien observers were located 5 billion light years away, our Sun wouldn't be seen by them because it didn't exist until an estimated 4.5 billion years ago.

Quote:
Originally Posted by Mark S. View Post
Yup. But to which I would stipulate: Define "life." We have a pretty decent definition of what that is here on Earth. Beyond ... things get a little more complicated.
I agree. Generally speaking our definition of "life" is based on what we know, which in turn is based on life on Earth. That's the only real model we have at the present time. As such, we assume that life elsewhere follows a similar model. In general, when we look at exoplanets that are thought to be rocky (as opposed to gas planets), we're also looking at candidates that are located at the right distance within what is called the "habitable zone" where water could be present in a liquid state, that the parent star is reasonably stable - conditions where life as we know it could potentially emerge. There are a lot more factors involved. Maybe life can emerge with such conditions, but there's no guarantee that life will always emerge under such favorable conditions.

Using the Drake Equation, it can be estimated that our own galaxy could be home to perhaps as many as 156 million civilizations, including highly intelligent civilizations. The downside to the Equation is that the factors it uses are limited. Other revisions of the Equation add in more factors and come up with different results. Of course, that still doesn't mean that all those additional factors will in fact produce life of any kind, or that all the conditions for life on Earth means life will always emerge elsewhere. We just don't know. We're still learning. We have a reasonably general idea about defining life on Earth, but even that's far from being a complete definition.
https://en.wikipedia.org/wiki/Life
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Old 09-22-2017, 01:48 PM
 
Location: Greenville, SC
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Quote:
Yup. But to which I would stipulate: Define "life." We have a pretty decent definition of what that is here on Earth. Beyond ... things get a little more complicated.
That's a problem we'll continue to have with life detection efforts in places like Mars or the moons of Jupiter and Saturn as well as outside the system. Life on Titan would be very alien for example -- different solvent than water (which is rock hard at those temperatures), different material for cell walls. But we can't even decide if things like viruses are alive on our own planet; everyone agrees prions are not alive, and bacteria are alive, but viruses are in a weird place between them -- neither fully alive nor fully inanimate.
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Old 09-22-2017, 02:23 PM
 
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Originally Posted by alaskaboy View Post
The science documentary I watched the other day said 55 billion years at the speed of light. The human mind can't even grasp that type of distance. In reality, it's like a non reality when you think about it.
The figure you mention was probably 56 billion light years in diameter, with a radius of about 28 billion light years in any direction from Earth, relating to the Observable Universe. But the Observable Universe could be as much as 92 billion light years in diameter, with a radius of 46 billion light years.
https://en.wikipedia.org/wiki/Observ..._universe#Size
https://www.space.com/24073-how-big-...-universe.html

Agreed, the numbers are mind-staggering, but it's not completely beyond comprehension to grasp based on current knowledge, techniques and equipment. I suspect that some views in the future may change based on newer information that's unavailable to us today.
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Old 09-22-2017, 05:26 PM
 
Location: Greenville, SC
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Quote:
Originally Posted by alaskaboy View Post
The science documentary I watched the other day said 55 billion years at the speed of light. The human mind can't even grasp that type of distance. In reality, it's like a non reality when you think about it.
Whether it's 30 billion or 55 billion light years across doesn't really matter. The argument you're making is the universe is so big that there has to be a civilization more advanced than us out there.

Possibility 1: we're it in the Milky Way, but there are advanced civilizations in other galaxies. The UK's version of Dr. Neil de Grasse Tyson, Dr. Brian Cox, points out there are a lot of accidents in the evolution of life on earth that led to us. There was only single-celled life for the first 2.6 billion years of earth's history. Then, multi-cellular life arose, likely (Cox says) because of a happy accident. If an asteroid had not wiped out the dinosaurs, the mammals wouldn't have become dominant. The dinosaurs were around for 190 BILLION years without showing any sign of developing high intelligence. So his argument is: we're it in the Milky Way, but there may be advanced civilizations in other galaxies.

Let's suppose there's a civilization in the Andromeda Galaxy that's more advanced than us technologically. Andromeda is 2.54 billion light years from the Milky Way. That means they wouldn't be aware of us for at least 2.54 billion years from now plus however long it takes for us to develop a high enough technology that our presence would be detectable from that kind of distance.

What that means practically is: we're isolated from other galaxies by extreme distance. They might as well not exist from our perspective - so pragmatically, we're alone.

Possibility 2: there are hundreds to a few thousand advanced civilizations in the Milky Way. Michael Garrett speculated at the International Astronomical Congress a few years ago that there are maybe 3,000 technological civilizations in the Milky Way. If this were the case, they'd be on the average 1,000 light years apart. Which means it will be roughly a thousand years before our nearest neighbor detects us, and if they send a message back, we'll receive it 2,000 years from now -- assuming we're still around.

What that means practically is: if anyone's out there in the Milky Way, it will be a few thousand years before we hear from them -- assuming they can detect our presence at all.

Possibility 3: there are a lot of highly technological civilizations in the Milky Way, and the closest one is close enough that they have received our radio and TV broadcasts from 100 years ago.

What that means practically is: we should have heard from them by now, since there are so many of them; that's the Fermi Paradox: if there are a lot of advanced civilizations out there, where are they?. Unless you assume they're avoiding us (which we have zero evidence for), we're left with Possibility 1 or 2.

I personally suspect Cox is too pessimistic, and Garrett is too optimistic. That would mean no one will realize we're here for tens of thousands of years, and a message from them would take twice that long. Imagining warp drive or "subspace" communication is an easy way out, but we have no more evidence those things are practically possible than that the Milky Way is full of Star Wars characters just dying to meet us. And I hope I'm wrong, and it's Possibility 3.

EDIT: Another interesting article on the topic with yet another opinion:

Quote:
Whitmire calculates that at this moment, if they indeed exist, there may now be as many as a million current tech civilizations in our Milky Way galaxy alone. But if his paper is correct, we will likely never meet them.

Last edited by Vasily; 09-22-2017 at 05:35 PM..
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