This Saturday will see a unique event in global science taking place far removed from any lab.

Hundreds of thousands of scientists and supporters will take to streets around the world to march in support of science, of evidence based research and of the truth.

The March for Science grew out of a visceral grassroots reaction to the early days of the Trump administration and its attitude towards science.

Social media chatter quickly flourished into an online campaign that in turn morphed into plans for a march in Washington DC.

That idea then steamrolled into a global movement that has resulted in more than 500 satellite marches not only around the US, but across the world, including here in Dublin.

The March for Science Ireland will begin at 2pm at Grand Canal Square, headed for Government Buildings.

Speaker will include Luke O'Neill, Professor of Biochemistry at Trinity College Dublin; Síle Lane, Head of International Campaigns and Policy at Sense About Science; and Aoibhinn Ní Shúilleabháin, Assistant Professor in the School Of Mathematics & Statistics at University College Dublin.

The marches are being framed as a backlash against widely reported threats from US President Donald Trump and his team against the independence of agencies such as the US Environmental Protection Agency, against research budgets and against well established evidence based research findings around areas like climate change.

Officially, however, the mission of the main march is to champion "robustly funded and publicly communicated science as a pillar of human freedom and prosperity," no matter which side of the political divide a threat might come from.

"We unite as a diverse, non-partisan group to call for science that upholds the common good and for political leaders and policy makers to enact evidence based policies in the public interest," the organisers say.

But in reality the movement is about something much more fundamental than this, or even than science itself.

It is about challenging an emerging post-truth world, where decades of work by many of our finest minds is being dismissed simply because a politician or powerful business person says they don’t believe it: A world where "alternative facts" go viral on social media without even being rebutted.

Climate change scepticism is an obvious example, as are anti-vaccine campaigns, many of which are increasing in prominence with potentially catastrophic effects for people.

The problem is that if enough people listen to and start to believe the minority of naysayers, whose utterances are often based on nothing more than groundless opinion, that sentiment can filter through to policy-makers and by extension policy itself, the march backers argue.

And the fear is that before we know it, the social media echo-chamber will have replaced the political debating chamber where legislation is crafted and approved they say.

Science has faced threats in the past.

But it is a mark of how serious scientists are taking the current situation and how under threat they feel that they have organised in this way.

Not everyone involved in science agrees with the movement or its goals, however.

Some say they won't take part in the marches because they have a problem with science becoming politicised in this way.

They argue science is apolitical, that its job is to establish facts and let politicians frame laws and policy around that.

Others, however, point to the inherent political nature of science dating back centuries to Galileo's imprisonment for heresy.

They also argue that in some cases they are even facing into an existential threat to their work as a result of funding cuts and threats of gagging them from communicating.

Like all grassroots movements, there are also those who take issue with the way the US March for Science movement is being run.

An early row about the nature of the march's diversity statement led to it being changed, satisfying some critics but annoying yet more who feel it reinforces the marginalisation of women and minorities in research.

Here, the organisers of the March for Science Ireland say their mission is broadly to support that of their colleagues in the US, but in an Irish context.

Backed by partners including the Irish Cancer Society, Irish Society for Immunology and Irish Federation of University Teachers, those behind the Dublin march say it has three broad aims.

These are to support and stand up for international collaboration and the sharing of scientific knowledge across borders, the adoption of evidence based policies and last but not least, a celebration and support for science in Irish society and culture.

In the backs of the minds of those marching here, however, there will no doubt be much more parochial concerns about Irish science policy: Worries about the need to increase domestic science funding, for example, as well as the ongoing calls for more support for basic research.

The reality though is that collectively, all these gatherings and movements are the first few steps in a long new science experiment.

Well after the final chant has echoed away to silence, the last weary and hoarse scientist returns home and all the pithy placards are carefully recycled, the threat will remain.

The post-truth era won't disappear overnight and this campaign will need to continue if it is to succeed.

The world is a different place now and science will have to reclaim its important place at the centre of it, if it is to survive and thrive. Something it must do for all our sakes.

Comments welcome via Twitter to @willgoodbody