Or, are there any organisms that fit the basic concept of “living” which don’t have DNA? If so, what do they have, and how do they qualify as living?
Some viruses contain RNA and not DNA. See Virus classification - Wikipedia
Whether you want to count a virus as a “living thing” is basically a semantic choice.
There are also self-replicating ribozymes, made entirely of RNA, and prions, which are apparently pure protein, though they may require a scaffold of RNA or other polyanions to fold properly - the jury’s still out on that. Both of those are pushing the definition of “life” quite a bit, though.
Are red blood cells alive?
From the field of astronomy we understand that the rate of the universe’s expansion is such that it must already be infinite in size. Earth has life, so the probability of a star having a planet circling it with life is greater than zero. Therefore, with an infinite number of stars in the universe, there must be an infinite number of planets with life, too.
While it seems hard to say with confidence, I think it is most reasonable to suppose that not all of these life forms on these planets use DNA, and there would be an infinite number of kinds of life that don’t use DNA…
Do we know this for sure?
No.
But to further Napier’s point, is how fascinating it would be to discover life elsewhere in the universe that doesn’t use the DNA/Double-Helix mechanism for encoding genes and producing organisms.
It reminds me of a very small line in E.T., when the government is swarming through Elliot’s house, and E.T. is on the bed dying, one of the random scientists exclaims, “He’s got DNA!” I really wonder what the probability for that is.
Even if the Universe is infinite in size, there still a finite amount of matter in the universe.
It’s not infinite, it’s just a really, really big finite number.
Personally, I’d be surprised. I’m sure there could be other systems that would work equally well.
I’m sure our sexy alien overlords will have TNA.
Back when I was in med school first year, “life” was determined by 4 criterions :
- Can move on its own
- Can reproduce itself
- Produces its own energy
- I don’t remember the 4th :(. I think it was about having at least one cellular nucleus, but I wouldn’t bet my life on the recollection. Although admittedly, that point would constitute a fairly geocentric definition of life, and constitute a circular answer to the OP. So we may ditch that one.
But virii don’t move, nor create or consume energy, nor reproduce on their own (they parasite cells and take advantage of *their *reproduction mechanisms to create more virii), hence they’re not living creatures by this acception. Neither are red blood cells (to answer another poster). Mithocondriae would be a more complicated matter, though.
I propose evolution is a good definition of life. If it has descendants that adapt to their environment over time then it’s alive.
It depends on your definition. They don’t reproduce and they’re part of a larger organism.
>Do we know this for sure?
As I understand it, the answer is yes, sort of. More precisely, in the current understanding of cosmology, the details that would weigh in on this question have all been confidently decided and the answer is, yes, measurements confirm, the universe is infinite. I think it is prudent, though, to note how widely theories have ranged in recent decades on this question, and to say that it is hard to confidently predict that we will not change our minds on this in the next few decades. So, if I had to decide now, I would accept the universe as infinite and the number of planets with life forms as also infinite.
>Even if the Universe is infinite in size, there still a finite amount of matter in the universe.
Todderbob, I’ve never heard such a statement and on the basis of what I have heard understand it to be incorrect. Why do you say this?
You can’t measure infinity. We can only say that we haven’t found any boundaries yet.
Infinity is not measured. It is determined. More specifically, no finite universe can become infinite so the presumption must be made that the universe was infinite at its creation (assuming it has one rather than being eternal). That means that the theoretical assumptions for how the universe was created determines whether it is infinite in extent or not.
Since there is no consensus on how the universe was created, its status as infinite or finite is dependent on the individual model used.
Whichever model is used, for all practical purposes no information can ever reach us about areas of the universe that are past light speed communication with earth, now or in the past. Even with expansion that puts an absolute limit of about 67 billion light years as the boundaries of our universe.
You can make theoretical speculation about what lies beyond that, just as you can speculate about multiverses with different physical laws than ours. But that has as much meaning today as speculating about the infinite number of shades of pink in the Invisible Pink Unicorn.
We’ve done this in a million other threads. How about not hijacking this one?
Because matter is neither created nor destroyed.
If matter is neither created nor destroyed, only converted. If there’s X matter in the universe today, there will be X matter in the universe tomorrow. No more, no less.
That’s still a finite number.
While the amount of space may increase exponentially, the matter will always be the same. If it’s always the same, it has a finite number. It may be an immessurably large finite number, but it is a finite number.
If this is true, then there are an infinite number of creatures named “Napier” out there; and an infinite number of them posting on message boards; and so on; so that there is an infinite number of people out who are arbitrarily similar to you, down to the thoughts going through your head.
No?
From the field of mathematics, we know that there are an infinite number of natural numbers. The number two is an even prime, so the probability of a number being an even prime is greater than zero. Therefore, with an infinite number of natural numbers, there must be an infinite number of even primes.
(Which is to say: one needs to be careful when making probability arguments with infinite sets.)