# Thread: The Scale of the Universe

1. ## The Scale of the Universe

From the Plank Length to the estimated size of the Universe. From 10^-35 to 10^27 meters. Marvelous.

2. Ah yes, I've seen this before - I believe I saw it linked on the Richard Dawkins website (in the forums) a year or so back. Extraordinary.

3. Pretty sure I've linked this at least a few times on the forums. Powers of Ten

4. O_o

That's disturbingly sexy.

Soma

5. Originally Posted by whiteflags
Pretty sure I've linked this at least a few times on the forums. Powers of Ten
Indeed. I remembered it just by looking at the title. It's a great little video.

6. This reminds me of a thread i was following on Reddit a month or two ago. It was about the likelihood of intelligent life (or even just life) in the universe, in regards to the recent advancements in exoplanet discovery (It seems having more than 1 or 2 planets in a solar system is quite common). One guy had constructed a very well formulated and very encouraging post. I'm not sure i can do it justice but i think it went something like this.

The observable universe contains approximately 300 sextillion stars (3 x 10^23). Now since a planet needs to have the right composition, size and distance from its' sun to be considered earthlike, let us be very very conservative and guess that one in a billion stars have an earthlike planet. If this estimate is correct this means that there is 3 x 10 ^ 14 earthlike planets in the observable universe, or put differently, there would be 300 trillion planets just like earth.

Now, since we have yet to discover another planet that is truely earthlike (some are pretty close but let's just be picky for the sake of the argument), and we have discovered a total of around 500 planets (the exact number might be a bit higher), this means that so far, we know that 1 / 500 planets are earthlike (Yes yes, the 500 we've found so far might not be representative for the entire universe), at the least. There is a long way to go from 500 to a billion so the final number of earthlike planets are likely much higher than 3 x 10 ^ 14.

With 300 trillion planets or more, just like our own earth, it would be practically impossible for us to be alone in the universe, statistically speaking. If that is not an intriguing thought then i don't know what is.

In the face of such large numbers and overwhelming probability, the notion that we are alone in the universe seems to be fantastically arrogant. It is awe inspiring stuff indeed.

7. That is formally known as the Drake Equation. First introduced to me by the Cosmos series.

8. Ah, but the Drake Equation isn't actually real science, it's more like pseudo science. Also the Drake Equation is only about _detectable_ civilizations in our own galaxy. Actually getting into contact with another civilization is quite another can of worms. Since our radio waves are limited by the speed of light, the sphere of systems where intelligent life would have to be present for us to communicate with them is many orders of magnitudes smaller than the entire observable universe, and thus the likelihood of such a civilization existing is equally diminished.

Screw you c, screw you.

9. Ah, but the Drake Equation isn't actually real science, it's more like pseudo science.
I never made the claim it was science. Nor would I consider it pseudoscience, as it makes no claims itself (that I'm aware of) to be truth.

Also the Drake Equation is only about _detectable_ civilizations in our own galaxy.
You are correct. I got a little excited and didn't read your post well enough.

However, just leave a few terms out of the equation and you'll arrive at the same idea you described.

10. Indeed! c is our bane.

You may like to read Shklovsky & Carl Sagan on Intelligent Life in the Universe. It's the deepest analysis to date on the probability on intelligent life out there. I's based on an earlier book from the Russian astrophysicist and co-authored by both scientists. It uses the drake equation as a starting point, but goes deep in analysis of every of its elements. It doesn't try to come up with a meaningful number either. Rather a probable range.

It's an excellent read. Offered to me by a former girlfriend on my youth. It's got chapters that outdated by today's knowledge. But still very inspiring to read and a good display of the 70s and early 80s scientific understanding. It's gone out of print since, but you can often find it used on Amazon.

11. Don't we have to first determine the probability of life occuring on an earthlike planet?
The fact that we are here demonstrates nothing in that respect (weak anthropic principle).

12. Well there is more to space exploration than finding neighbors, so no, we don't.

13. Some would argue, correctly I'd say from all I understand of probabilities, that the probability of life occurring on Earth was 1:1, exactly because we are here. But mind you, the Drake Equation should not include that probability for the simple fact it is exactly an equation that tries to answer that probability. That is the probability of life on earth would is on the right side of the equal sign, not on the left.

But, for all that matters, we tend to look at alien life as having the same building blocks as life on Earth, which is clearly a potential mistake. Science has still to completely free itself of its anthropocentric roots. There's no real scientific reason to assume all life is carbon-based. The fact we recently discovered a possible arsenic-based DNA life form (this discovery is being seriously contested) here, of all places, on our until recently exclusive carbon-based planet, should be at least an eye opener.

In the realm of pure speculation, it's possible to even argue that we may not recognize certain alien life forms even if they were under our noses. A silicon-based life form for instance could exist in such a distant biological and metabolic set of rules from that we are used to, that we may be looking at one and think its just a rock (and probably as far as carbon-based life forms are concerned, that's exactly what it is). It's not until "recently" that we understood plants as being living beings. Some 5 years ago we are discussing whether plants have dignity too and whether it should be respected on countries with constitutions that approach it.

To me personally, it's clear we cannot rule out the possibility of alien life-forms being based on other fundamental constituents. In that context too, the probability of life on earth would be non consequential to a Drake equation.

EDIT:

An argument can be made though that those life-forms are of not interest for us. That we are looking for life-forms with the same building blocks because that removes a whole lot of difficulties from that search. The general idea is if we cannot recognize a rock as a living being, a practical man would say let it be a rock then.

But... careful! We cannot address an extreme possibility by removing all the ones in the middle. An alien life-form made of arsenic (which is highly toxic for us) is a particularly important finding. Especially if it turns out to be intelligent and technologically advanced.

14. Originally Posted by Mario F.
Some would argue, correctly I'd say from all I understand of probabilities, that the probability of life occurring on Earth was 1:1, exactly because we are here.
That doesn't sound right, to me that sounds like winning the jackpot on your first and only lottery ticket and after that conclude that, the fact that I'm a winner means that the probability of winning is 1:1.

15. > From 10^-35 to 10^27 meters
Mmm, given that every scale has something in it, I wonder what lies in the gaping chasm of 20 orders of magnitude between the smallest known size and the plank length.

It's like saying the smallest thing is a proton, and the next smallest thing is a small moon.

It could be a while before we find out as well - it seems to take about a century to get through about 3 orders of magnitude.