The Instigator
Pro (for)
1 Points
The Contender
Con (against)
3 Points

THB: Extraterrestrial life exists

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Post Voting Period
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after 1 vote the winner is...
Voting Style: Open Point System: 7 Point
Started: 4/13/2017 Category: Science
Updated: 3 years ago Status: Post Voting Period
Viewed: 1,554 times Debate No: 101944
Debate Rounds (3)
Comments (5)
Votes (1)




[reposting because someone accepted but then never posted an argument. Please do not accept the debate if you are going to fail to post any arguments]

R1: Definitions, acceptance, pronoun introduction. No arguments should be offered. Any arguments offered should be ignored by voters. The definitions provided by pro will be the definitions used for the duration of the debate- Con needn't provide definitions, unless they are for a word which Pro has not yet defined.
R2: Main body of argument. Con may add rebuttal.
R3: Rebuttal and summation. No new points may be offered. New points argued in R3 should be ignored by voters. New rebuttal may, however, be offered.

Please use she/her pronouns for me. I will default to using "they" pronouns for anyone else unless I am told otherwise.


"THB": Abbreviation for "This house believes" i.e. the claim being argued.
"Extraterrestrial": Originating from a planet other than Earth.
"Life": Anything capable of "MRS GREN" (see source 1 for explanation).



Now assuming from the website you have cited in the first point of your debate and the stigma that surrounds the title of this debate, I am taking the standpoint here that we are discussing the pints of view that intelligent life could exist somewhere in the Universe, and the answer to this question is that the chances of this happening are in fact very unlikely. Now of course there are Government institutions such as SETI set up and designed for this search of alien neighbors which may possess the intelligence required to communicate with the human species. However, outside of our solar system, it is extremely difficult to identify where this alien life could settle. Key astronomers have pointed out planets in other systems, light years away, which may possess the ability of possessing alien life. However to manage and sustain life, there must be key points which must be addressed in an atmosphere and planet's surface, in order for life to flourish. According to the Drake equation, there are an estimated 60 billion different planets in our universe that could possibly have the potential of supporting some sort of extraterrestrial life. Now this does seem like a significant amount but every single thing that we hope to understand must be taken in relation to a key context. Now within our known universe there are approximately 100 billion galaxies. Within the Milky way there are 100 billion estimated stars, and assuming there are around 8 planets within a solar system, we can assume that there are 800 billion planets within our galaxy alone. using the approximate 100 billion galaxies, we can use mathematics to calculate that there are around 80000000000000000000000 planets within our known universe. To take the idea of this and divide it by the number of planets in which Drake's equation predicts can hold alien life, we see that only 0.00000000000075% of the planets within the know universe could possibly have the mechanisms support alien life. The chances that life came to the way it did on Earth has a mathematical probability incredibly low also. Taking this into account we can see that if we had one single bacteria, that would randomly be allocated to a planet. If it were to land on the planet that could support life, it would begin to multiply to form multi-celled organisms and continue to grow until life prospered. The bacteria would have the very long percentage chance which I said of reaching a planet which could support it. On top of this the percentage would lower as to whether the bacteria could in fact multiply into more organisms and finally, the chances go further down because of the fact that the planet may not be hospitable for the organisms which the bacteria evolves into. However, there is this constant argument that it happened on Earth and it did. We somehow, went through all of the chances and now we are here debating this topic. However, seeing our chances of existing as this percentage is hard enough to comprehend, but to believe that life similar to us, that can build major civilisations is almost beyond contemplation. The chances of winning the lottery are one in 14 million. The chances of being life on another Goldilocks planet would be the equivalent of winning the lottery for every single day for a whole week. Whilst the mathematics show it is possible, we can see that this applies to the state of the Earth. In order to see other planets, this means that you would have to take the equivalent of winning the lottery 14 days in a row. Again, the mathematics show that it is possible, but is it likely, the answer is a very stern no.
Debate Round No. 1


Con has presented arguments in R1, contrary the rules outlined in R1. Hence, I have not read their R1 comments, and neither should voters (or voters should disregard Con's R1 comments if they have already read them).

This conversation should be considered a probabilistic argument; I cannot prove 100% that extraterrestrial life exists, but nor can Con prove that it does not. However, I will attempt to argue that it is overwhelmingly more likely that extraterrestrial life does exist than that it does not.

I will do so by producing a lower bound (i.e, an underestimate) for the probability of life existing.

There are at least 10^22 (100,000,000,000,000,000,000) stars in the universe (See source 1). The universe is over 13 billion years (see source 2) old. Now, let's assume that it takes 1 year for anything to happen, and only 1 thing can happen in a given solar system at any given time. This would mean that the number of things that have happened are (10^22)*(13*10^6) ~ 10^29.
This is a severe underestimate, but we've shown that at least 10^29 things have happened in the universe since its beginning.

Let p = the probability of life being created by any single event. We can demonstrate that life is overwhelmingly likely to exist by calculating what the odds of a given event creating life would have to be in order for the probability of life existing to be as high as it not. i.e.:

(1-p)^(10^29) = 0.5

Rearranging gives:

p= 1-(0.5^(1/(10^29))) ~10^-30

(See source 3)

Now remember, p is the probability that life is created by any given event, and we have shown that it would have to be less likely than 10^-30 for the chances of life existing to be less than or equal to the chances of it not existing. This is equivalent to winning the lottery four times consecutively, when buying a single ticket each time- life-creating events would have to be extremely uncommon for life to not exist somewhere else in the universe, and all of this is underestimating the chances of extraterrestrial life (and thus overestimating the chances of it not existing).

Another way of thinking of this is to imagine the chances of life existing are, say, one in one million million million.

That would make the probability of life existing:


= 1 to a ridiculously high precision (See source 6). Another way to think of the result is that the probability of life *NOT* existing somewhere else in the universe if we make the above assumptions is:

~10^(-43429448191) (see source 7)

This is equivalent to winning the lottery 5428681024 times consecutively, when buying a single ticket each time (see source 8).

So, the chances of extraterrestrial life NOT existing if we make the above assumptions are 5428681024 to 1: a ridiculously small amount.

In a single sentence: The universe is so extremely large and has existed for such an extremely long time, that the probability of extraterrestrial life is so extremely high it is difficult to comprehend.

[1}: "With this simple calculation you get something like 10^22 to 10^24 stars in the Universe."
[2]: "In 2012, WMAP estimated the age of the universe to be 13.772 billion years, with an uncertainty of 59 million years."
[4]: "1 in 13,983,816."
[5]: "7.15112384e-8"


I apologise for the mistake made in the round one comments, this is down to my error of not reading the rules of the debate with clear precision. However, my opponent has also made a clear error within their first argument here. The party arguing for the motion, and myself also in my first, disregarded statement, have debated an entirely different motion to the one outlined here. We have both argued for the motion of "Could Alien life exist". Using the mathematical probability here anyone is able to say that it could exist without any form of scientific proof. Using this same argument we can say without certainty that God exists, flying saucers exist, and the great spaghetti monster of the east could exist, purely for the fact, that the maths cannot be disproved to 100% certainty. The real point in which we are debating is "does alien life exist", through the clear title of "This House Believes Extraterrestrial life exists". If we argued could it exist, I would say yes, but "does it exist" is entirely different. Every point outlined in your Round 2 argument clearly states that you believe that alien life could exist, but you have in no way provided reasonable evidence for your belief that it does exist. To determine whether something exists with 100% certainty, we must be provided with irrefutable evidence for the existence of the object in question, and I am sorry to say that there is no such evidence that can be provided for the existence of Extraterrestrials. There is however, suggested evidence for their existence but these can be simply dismissed with a few key arguments. There are 3 clear arguments given as to why alien life exists through the evidence. The first is cave paintings, found in caves throughout the world. Primarily found in Egyptian hieroglyphs, these depictions show strange looking men, with large heads, large eyes, matching many descriptions by eye-witnesses of what they believe to be aliens. Caves found in India have also been suggested to show these same things but upon closer inspection, it is clear to see that these may just be artistic interpretations of humans and maybe even deities that these people believed in. If we are to believe that Ancient peoples interacted with aliens simply because they drew them on their walls, we must believe in all deities ever drawn by the ancients, as they must have encountered them too. (See source 1 for Indian cave paintings). Secondly we look at the evidence of eye-witness testimony, of people who have seen aliens, UFO's and even report to have been abducted by these beings. We cannot take simple eye-witness testimony as argument that something must exist, because a select few people have seen it. Again, in this same way we would have to believe in the existence of ghosts, Sasquatches, werewolves, vampires, etc. all because a select few individuals report to have seen them. Eye witness testimony is also something which can also be largely skewed by individual factors. Tests done by Loftus and Palmer have shown that peoples reporting of an incident can be skewed based upon leading questions performed by the interviewer. They found that people witnessing a car crash, reported the cars as going at a faster speed, when the verb used to describe the incident was more violent, escalating from contacted to smashed. (See source 2 for article publication). When looking at these interviews, it is clear to see major biases in the research which skew results. There exists investigator biases, making individuals want to give answers to help the researcher, many hoaxes relating to the issue, the fact that in many cases of hypnosis interviews, many of the individuals had read at least one or two more books relating to the concept of abduction. (See source 3 for data). Finally we come to video evidence and pictorial evidence for the existence of aliens and UFO's. Firstly we come to the videos of UFO's, easily faked videos usually lasting approximately 30 seconds to 1 minute. Shaky footage of a piece of metal in the sky is not concrete evidence for the existence of alien life. Similarly, the movement of random lights in the sky is not evidence either. The definition of UFO is "Unidentified flying object", meaning that the objects in this videos have the possibility to be anything without being craft piloted by alien life. If something is classed as "unidentified" you cannot claim it to be something without clear and justified evidence. Finally, we come to evidence from outer space, evidence which does not exist. We have found no evidence, let alone concrete evidence, of any life beyond our planet Earth. Despite rigorous searching and studies, there has not been any evidence for Extraterrestrial activity within the known universe. Using mathematics only proves that something may exist. Until there is solid and published evidence that alien life exists and can prove beyond a reason of a doubt that other claims are false, then nobody can state that alien life exists. To justify any claim you need evidence, and since there is no evidence for alien life to this date, the claim that there is, is unjustified and until I am disproven, it is false.

Source 1:
Source 2:
Source 3:
Debate Round No. 2


It seems some of the links I used as sources in R2 don't work. For those links, please copy the expression I was sourcing a value for (e.g. " 1-(0.5^(1/(10^29))) ~10^-30" for source 3) into Wolfram Alpha (which is sent by the link).

In the interests of making refutation easier, I have condensed Con's argument into manageable points:
1) My (Pro's) R2 arguments didn't address the motion- it doesn't try to justify a 100% certainty in the belief that alien life exists.
2) Ancient cave paintings of what are supposedly aliens may not actually be depicting aliens.
3) Eyewitness testimony is unreliable.
4) Video evidence can be faked.
5) There is no definitive evidence from space of extraterrestrial life.

In response to point 1), my argument does address the motion because, as I specified, I have argued (in my view, quite convincingly) that it is overwhelmingly more likely that extraterrestrial life exists than that it does not. Doing so does indeed justify the claim that "This house *believes* extraterrestrial life exists", as the motion doesn't claim certainty. If one considers a claim to be more likely to be true than to not be true, one *believes* in that claim, as per the wording of the motion. Had the motion been "This house knows to 100% certainty that extraterrestrial life exists", I would have failed to address it. However, this is not the motion being discussed.

Points 2:4 are essentially refutation to arguments which I never put forward in the first place; The majority of extraterrestrial life is most likely microbes or similar mono-cellular organism- the motion never proposed *sentient, humanoid* life, although I believe a similar probabilistic argument could be made in favour of such a notion.
It may very well be the case that cave paintings were never meant to depict aliens, that all eyewitnesses of extraterrestrial life on Earth are lying or delusional, and that all video evidence of UFOs is faked, but none of this would make my probabilistic argument in R2 any less valid; it is overwhelmingly likely that extraterrestrial life exists that has never made contact with humans.

In response to 5, I'd like to point out that there is considerable evidence that may point to extraterrestrial life: the ALH-84001 meteorite (see source 1) is one such example. However, even if there were absolutely no evidence for extraterrestrial life [NB: there is], that wouldn't necessarily mean such life does not exist; imagine a form of extraterrestrial life on a body orbiting a random star in a random galaxy in our universe; the odds of it being within range of our detection are unimaginably small, and the odds of it being in our solar system- as would be necessary for us to expect considerable evidence for such life- are even smaller. Absence of evidence is not necessarily evidence of absence, especially in cases where one wouldn't necessarily expect evidence to be present if the claim were true. I'd also doubt Con's claim that:
"To justify any claim you need evidence"
There are some things we can know "a priori" (see source 2), meaning that we don't need to establish them with empirical evidence and observation. One such example is the claim that "All bachelors are unmarried"; by definition of those words, it must be true- no evidence needed. Likewise, probabilistic statements like the one I'm making (i.e. that it is more likely that extraterrestrial life exists than that it does not) do not need to be backed by empiricism, and approximations and mathematical deductions such as the ones I used are valid to establish a probabilistic claim.

Myself and Con agree that extraterrestrial life may exist. I feel I have argued convincingly in R2 that it is overwhelmingly more likely that it does exist than that it does not, and I feel Con has failed to refute this. Hence, we should believe that it does exist. Hence THB extraterrestrial life exists.

Thank you for your time.

[1]: "NASA scientists and their colleagues announced they had spotted possible signs of Mars life in a meteorite."
[2]: "relating to or denoting reasoning or knowledge which proceeds from theoretical deduction rather than from observation or experience."


To begin I have to comment on the notion of the question for debate once again. The points that were made by my opponent during Round 2 of the debates does have some very good points pertaining to the idea that alien life could exist, but once again the question remains unanswered. The mathematics have shown through my opponents calculations that it is very unlikely for aliens to not exist, but this still leaves an area of disagreement, with the maths still showing that it is entirely within the realm of possibility that no alien life exists anywhere beyond our realm of knowledge. This means that overall your argument does make the clear point that alien life is very likely to exist, but this does not support your claim that it does, beyond any reason of a doubt exist, as there is still an area of your argument which clearly states that no alien life could exist whatsoever. Just because something it is extremely likely to be true, does not mean that it has to be true as a result. Improbability does not imply impossibility. Meaning that just because it is very improbable that there is not life anywhere else, it is not impossible that we may be the only intelligent beings in the universe. Your argument is indeed good and very thought provoking, but it cannot justify beyond reason of a doubt your claim in the belief that alien life exists.

On to your next point of rebuttal. You claim that my points are refutation to ideas that you had never put forward, which is true to some extent. Within your round two argument you never stated that these forms of evidence were proof of the existence of alien life. However, these points make a very relevant comment on the ideas that you put forward. All of the ideas of cave paintings, eye witness testimony and video footage are suggested physical evidence for the existence of extraterrestrial life. However, in your round 2 argument, you put forward no evidence whatsoever. Your entire summation of your argument says that "The Universe is so extremely large and has existed for such an extremely long time. that the probability of extraterrestrial life is so extremely high that it is difficult to comprehend". You summarise your whole argument based on the concept of likelihood of an event. As I stated earlier in this rebuttal, just because something is improbable, does not mean that it is impossible. This idea can not only be applied here, but it can be applied to every day life. Using mathematics I could make a wide range of statements to show that something is very likely. Mathematics based around my health, the area where I live and other factors could show to a very high degree of probability that I will survive the next hour coming, but I cannot say that this has to be true because the probability of me dying is so extremely low that it cannot be comprehended. You make the claim that I use the absence of evidence as an argument that they don't exist, to some extent I do, but there is a level of a similar action here, with my opponent stating that because the probability of there being extraterrestrial life is so high that we cannot comprehend it, this means that there is strong support for the claim that it exists, which I am afraid to say there is not.

Now referring to your claim of multi-cellular organisms. In your opening statement you made reference to the biological concept of MRS GREN, a system of seven criteria to determine whether something is in fact a living organism. Now pertaining to your idea of these being alive, yes they could be according to this idea but this is only one concept of what it actually means to be alive. In order to answer this we must look into basic philosophy and see whether it is classed as alive based on these ideas, as there is a very big contrast over whether these cells can be classified as alive. There is a big debate largely surrounding abortion (which is a debate for another time), in which some argue that a fetus is not alive until some weeks into the pregnancy, despite the fetus being a collection of cells at this point. To have something be 100% true it must be proved beyond reason of a doubt and to see that there is still clear debate amongst people as to whether it is alive, this idea of MRS GREN must be postponed until there is a common agreement about the human interpretation of when something is alive and when it is not. As such it is hard to say with 100% clarity that any bacteria or other cellular level organisms in space can be counted as clear evidence for life when there is this widespread disagreement. This means that our debate is restricted to this concept of humanoid and sentient beings at this point in time.

You also use the ALH-84001 meteorite found in Antarctica as an example of evidence that points to there being alien life. Now when first discovered the researchers believed there to be evidence of bacterial fossils from mars on the rock, but these were very controversial claims, and in fact, the wider scientific community rejected these claims after further study of the meteorite, making it completely redundant as evidence of anything other than a meteorite that has fallen to earth. Now there is this common theme amongst believers in extraterrestrials to say, there is evidence, you just haven't looked closely enough, as said in a much more polite and professional way by my opponent here than by many others I have had this debate with. I did some research around cases similar to the meteorite in which you spoke of and all of the evidence that has been used by my opponent's side of the debate all share an extremely common theme. They are all controversial. Not a single piece of evidence found can say to a great level of certainty that it is evidence of alien life. The meteorite was argued against by the scientific community, the Wow signal has not be proven to be of alien origin, mars landers have not been able to gather the same results as the Viking lander which apparently gathered evidence of bacterial life in the soil. There is not one single piece of credible evidence that points to alien life existing as of current. This spawns another debate question of, if alien life cannot be proven to exist, does it belong in the realm of science, or should it be paired with more philosophical concepts such as the ideas spread by religions.

Now my opponent says that if we were to imagine life on a small world orbiting a star beyond our range of detection, that the life would exist but we couldn't detect it. Now this is a very common argument and it is one that is hard to debate against because it is almost an unanswerable question, similarly again to the way in which religious people argue that we cannot find evidence for God because it is beyond human detection and comprehension. This is not a supporting claim for extraterrestrial life existing. It is not evidence or scientific reasoning to say that something exists purely because we have not found it yet. On the contrary it is much more reasonable to say that we have looked for evidence of this object and we cannot find it, meaning therefore that we can conclude that object x cannot exist. Whilst it may be true to say that an absence of evidence is not an evidence of absence, it is more logical and reasonable of an argument, than saying object x is likely to exist, we have found no concrete evidence of object x, but this is simply because our science is not good enough to find it yet. If our science is not good enough to find evidence for your claims, then you have no possible realm of evidence to support your claims.

We come to your rebuttal about my statement, to justify any claim you need evidence. You say that there exists a priori, a statement that does not need to be supported with factual evidence to know it to be true. Now this is true in today's society, it is fair to reason that "all bachelors are unmarried" because this is something that we know to be true. However, my opponent ignores the clear evidence behind each component of that claim that has led us to be able to say that without evidence. We had to define the term bachelor looking at people in our society who were unmarried and have never been married in their lives. In order to give them this title we had to observe the actions and behaviors of individuals and be able to conclude that scientifically, all bachelors are unmarried. Without having previously observed and defined this term using reasoning, this would not be a priori. Now this concept is very similar in science, known as a paradigm. Paradigms are a set of shared assumptions and agreed methods within a certain discipline. However, just because something is widely accepted to be true, does not mean that it is. Paradigm shifts often occur in science that lead shared assumptions to change. Early in human science, it was believed by scientists everywhere that everything orbited around the Earth. After further research this assumption changed to the now universally accepted idea that everything orbits around the sun, after concrete evidence proved it beyond reason of a doubt. Up until the work of Charles Darwin, everyone believed, in science, that man was created by God in his image. The work of Darwin and other scientists has proven, beyond reason of a doubt using evidence, that we evolved over a very long period of time. All widely accepted assumptions are based on some form of observable evidence. This means that my use of the phrase"to justify any claim you need evidence" is in fact true in the realm of science, the only field which could possibly provide clear evidence of alien life, which it has proved, beyond any reason of a doubt, that it cannot do. Your probabilistic claims do not need to be backed by empiricism, but this does not make them fact, they are simple estimates that cannot be used to prove anything.

Pro has failed to prove beyond reason of a doubt that her claims are true, meaning that they cannot be taken as fact.
Debate Round No. 3
5 comments have been posted on this debate. Showing 1 through 5 records.
Posted by whiteflame 3 years ago
>Reported vote: byaka2013// Mod action: Removed<

2 points to Pro (Conduct, S&G). Reasons for voting decision: T

[*Reason for removal*] Not an RFD.
Posted by whiteflame 3 years ago
>Reported vote: samsun01// Mod action: Removed<

7 points to Con. Reasons for voting decision: Think Con is right.

[*Reason for removal*] This is not an RFD. The voter is required to evaluate the debate, not merely to provide his own generalized views of one of the debater"s arguments.
Posted by PowerPikachu21 3 years ago
Site lagged. Sorry about the double comment.
Posted by PowerPikachu21 3 years ago
[Addition to RFD]

Pro did have one piece of evidence; the ALH-84001 meteorite. However, Con pointed out it's not conclusive evidence. I'm not really sure how to vote on this debate, since neither side seemed to prove a 100% certainty, which is kind of what these "do aliens exist" rely on, in my opinion. If I missed something, let me know so I can update my RFD.
Posted by PowerPikachu21 3 years ago
[Addition to RFD]

Pro did have one piece of evidence; the ALH-84001 meteorite. However, Con pointed out it's not conclusive evidence. I'm not really sure how to vote on this debate, since neither side seemed to prove a 100% certainty, which is kind of what these "do aliens exist" rely on, in my opinion. If I missed something, let me know so I can update my RFD.
1 votes has been placed for this debate.
Vote Placed by PowerPikachu21 3 years ago
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Total points awarded:13 
Reasons for voting decision: Whew. So the resolution was "Do aliens exist"? However, we can't answer this question with 100% certainty, as both Pro and Con noted. Because of the lack of evidence, Pro needed to use math to prove that aliens are very likely to exist (an argument I do believe in). However, as Con pointed out, that's only the possibility they exist. Pro's explanation is that she doesn't need to prove 100% certainty, but the definition of "THB" didn't really cover that. Who is "this house"? Pro attempts to argue that evidence isn't needed to reach a valid conclusion by saying "all bachelors aren't married". Con points out that the definitions are in fact evidence. The truth is, we'll never get a definitive answer, to this question. Burden of Proof usually falls to the one making the debate, which is Pro. She was unable to give certainty to the existence of extraterrestrials, so I'm voting Con. However, Conduct to Pro since Con ignored the rule to not post arguments R1.

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