How does science reach a consensus? How do we know the age of the earth? How do we know that all creatures on the planet evolved from a common ancestor?
The shorthand answer is, we just do, because many people before us have done countless experiments in order to come to the scientific conclusions we have arrived at today.
However this answer is not very satisfactory to the enquiring mind, and nor should it be. Because if a person is to accept the above statement without question, then that simply leaves the door open for any old theory to gatecrash your mind, with the permission slip of because I said so.
I started this series with an article regarding a flat earth documentary called Behind The Curve. The documnetary is disturbing in that people who are apparently trying to find out the truth, completely ignore that truth when it doesn't align with their beliefs.
I postulated that the reason why somebody is so ready to dismiss the results of an experiment that they themselves ran, had to do with a lack of reasoning skills, rather than a lack of knowledge.
Reasoning is about looking at your own beliefs and judging them objectively using experiment and observation to try and disprove those beliefs. It is only after several tries at disproving your own theories, and cross-referencing your results with those of others, that you can finally say whether you're right or wrong.
I invited people to debate me, as I wanted to do what the NASA scientist on the documentary suggest we all do, and that is to reach out to people with views that wildly differ from accepted reality, and offer to debate them in a calm and polite manner.
After reading and replying to some of the people on that article, I wanted to create a post explaining exactly how the scientific consensus is reached, because a lot of times, to the outsider it may seem like complete guess work.
However my esteemed colleague 
So apart from a few corrections for spelling mistakes, and also a couple of adjustments for reasons of context, I decided to reprint his answers in full.
History Of Science by
First, there is no such thing as historical science. All science is based on observation. Based on the observations, models are made to make predictions and theories are structured to explain what we see and suggest how the world works.
Again, based on observed facts. Theories then grow in strength over time as
It survives continuous efforts to falsify key assumptions that must be true for the theory to hold. And
Further facts are discovered that aligns with the assumptions of the theory. Both contributing to decreasing the likelihood that we’ve arrived at the theory by mere accident.
So just a quick example here, Darwin said in his book; On The Origin Of The Species, that if he found any frog spawn on remote islands, then his entire theory would come crumbling down. As this would prove that things like amphibians could spring up independently without means of transporting their eggs.
Since the invention and continued improvement of computers, we have been able to study DNA and confirm many assertions of the theory of evolution which fit perfectly with Darwin's predictions.
So, if I say that humans and chimpanzees share a common ancestor, or that the world is close to 4.5 billion years old, those statements are based on observational science. I didn’t have to be there to make the observations. I can make them today and still know that it happened.
As for carbon dating [the comment is in response to somebody questioning the validity of carbon dating], I’ve heard what you said many times before from people who deny the evidence for an old earth or for evolution.
But it makes no sense to even bring it up since [geologists] don’t rely on carbon dating to estimate either the age of rocks nor of fossils (it is useful when you dig up remnants from older human civilisations like from the Viking era, Roman era, etc that are more recent).
Instead, when an archaeologist discovers fossils that are very old, they will instead examine the rocks above and below the fossil-containing elements such as potassium with a half-life time of 1,250,000,000 years.
Today, millions of fossils have been documented, and the location of their discovery with regards to geological layers has always fitted the model of evolution and with [it] the estimated age of the earth. In other words, we’ve never found rabbit bones in the Pre-Cambrian.
Now, you may say – and indeed did say – that perhaps these laws may have changed. After all, we were not there to see and observe, right?
Well, there’re two issues with that. First, we have now relied on these methods for decades and they have not changed one percent of one percent (such a change would have actually added many meters [of] inaccuracy over time to our satellites which rely on atomic clocks due to the fact that they never change).
Second, this is not intellectually honest, and you are doing exactly what the people in the documentary are doing, which is to respond to evidence contradicting your beliefs by coming up with some alternative explanation – for which there is no evidence – in order to not have to change your mind according to new observations.
If you are going to always ask “but what if”, then you are never going to change your mind and never going to learn anything. Because you can always resort to saying that.
I don’t think I can put it better than Bertrand Russell when he gave his thoughts on it here.
So finally, how come I am so confident to say that I know that evolution [is] true and [what] the age of the Earth [is]? Because we have completely independent branches of research that support the same theory and because the resulting model allows us, continuously, to make accurate predictions of future events.
In genetics, we can now look at the DNA of different species and literally count our way back to the common ancestor. Computers have done this now for millions of species to make cross-examinations and judge how old a species is and how long ago it is since it shared a common ancestor with any other of the millions of species. The result can be plotted as a family tree. Guess what? It matches, perfectly, with the tree you get based on the dated age of all the discovered fossils.
So what is the likelihood, not only that each of these would produce consistent results on their own, but jointly by accident? It’s about as likely as you are winning the lottery every single week for the rest of your life, and then realising that everyone in the [United] States chose the exact same numbers when choosing theirs at random.
Except, I haven’t even mentioned the also confirming evidence from RNA, geological distribution of species and how they match continental changes etc.
So yes we can know these things, no we don't need carbon dating to know them (which you're right about) and no there is no such thing as historical science, models that accurately predict the future should be used to assume the past until otherwise is proven.
This next reply is in response to a statement that said thousands of scientists disagree with
No, thousands of scientists do not disagree with that. Or at least you'll have to provide a source for that claim, instead of just asserting it and expecting me or others to take it seriously.
Being "there" doesn't make a difference. The evidence is just as overwhelming as I laid out in great detail. I have not been to the future either, but I can tell you for sure - 100% - that on the 26th of May 2021 we will see a total lunar eclipse (or often called "blood moon") that I invite anyone of you to note in your calendars and then go out and witness.
I don't need anything but knowing that the laws of gravity stay fixed, [just] like radiometric dating, to be sure this will happen.
I'm also curious if you don't think we could ever gain knowledge about something like a murder without having eye-witnesses.
If a detective arrives at the scene of a crime, and make all sorts of discoveries that all point in the direction of a certain answer as to who committed the crime, then that is evidence. Likewise, I don't need to observe day-by-day evolution taking place, or the formatting of the earth to know a lot about how it happened.
Last point. The burden of proof is on you, or any other "scientist" who would argue that the many natural laws demonstrated to make accurate predictions going forward can somehow not do the same looking backwards.
As they continue to be robust and independent branches of science from biology, chemistry, geology, etc, confirms the same models, the default position is that they can. If we are to form our believes based on what is most likely to be true, and not on what we wish to be true, then this should be our frame of mind.
Consensus Reached by
You keep repeating that, but it doesn't matter. It's not about the numbers of people who believe X, Y or Z, but about what the evidence tells us.
I have provided evidence for my statements, you have not replied to either of my comments addressing the points that I've made, or suggested why they are not sufficient to prove the theories. Instead, you resort to telling me that someone disagrees, which is not an argument.
In case you're not aware, I've spent the better part of my working career in the space sector working at the European Space Agency (Europe's equivalent of NASA).
Working with astrophysicists who can calculate the age of the Universe and the distance to stars and galaxies with measurements relying on the consistency of the speed of light travelling at known speeds which allow them to know the distances between them, again adding evidence to an old universe.
I've been working with geologists and geophysicists making research instruments for experiments that are to be sent to Mars or different asteroids, as well as research results from previous probes.
These too, have provided insight into the age of the solar system and the different planets as well as the building blocks that make up our own.
I work with biologists and chemists creating experiments, or again analyzing results from old ones, to study how life can have originated, been possible on other planets, or perhaps existing there today.
Literally 100%, not as in "most" but as in every single one, of the people I've worked with here. -which are in the thousands for the space agency alone - not just "believes" that the Earth is approximate ~4.5 billion years old, the Universe ~13.8bn, that life has evolved etc, but continues to make progress with models holding those assumptions, which would be impossible if it wasn't true.
* * *
So what we can surmise from
They discover something, study it, and then come up with a hypothesis, then many other scientists from different disciplines, all study that thing as well, and make predictions.
Each time a prediction proves correct, the hypothesis moves on, until it finally becomes a proven theory. However another branch of scientists will try and disprove the theory in order to come to an even greater understanding.
By behaving in this way, we stay true to the original purpose of science, which is to make sure the things we think are happening, really are, and we are not just fooling ourselves because we wish reality to be a certain way.
WHAT'S YOUR TAKE ON HOW SCIENTIFIC CONSENSUS IS COME ABOUT? DO YOU TRUST SCIENCE? IF NOT, WHY NOT? HOW DO YOU COME TO A CONCLUSION WHEN ASSESSING A PROBLEM?
AS EVER, LET ME KNOW BELOW!
The Edge Of Reason - series so far:
The Edge Of Reason: Death By Connectivity
Title image: Lucas Vasques on Unsplash