THE rows of family faces at the dockside are tearful, or grim. They look up at the high railings of a huge ocean liner. Hanging over them, much younger faces also wave and mostly cry – though a few are already looking steadily out to the high seas.

For the heroine at the centre of the screen, and her relatives below, this is a terrible moment. Like tens of thousands of other young Irish people in the 40s and 50s, Eilis has been given the chance of a better life in America. The machinations of the Irish diaspora have arranged a job and lodgings for her in deepest Brooklyn.

Yet as the boat slowly moves off, the enormity of the decision becomes clear. The bright older sister will be left behind to her small-town bookkeeping job. Along with her frail, near-broken mother, they will both survive on letters and photographs; on rare visits that can only be financially justified as the fruits of real success.

But however stricken she looks, Eilis is off to a new life. Will it become a new home?

There are many pleasures to be taken from Brooklyn, the meticulous film adaptation of Colm Toibin’s novel, with the luminous (and Oscar-worthy) Saoirse Ronan as the young migrant at its centre.

But one is certainly that its story cleaves tightly to the strict social and physical limitations of its era.

The drama revolves around the flutter of airmails, a random encounter with a compatriot at a registry office, a visit back home that can’t speedily be escaped from, a dramatic single phone call in a wooden booth…

The emotions of Brooklyn depend mostly on how massive and intimidating the distances are between home and emigre; how severed or faltering their lines of communication; how sheer absence makes every little scrap of presence supercharged.

In our current era of relentless migration and movement, whether at a family or a continental level, does an old story like Brooklyn have much resonance? At least we can say, surely, that technology makes the separation of the ambitious loved one from the homestead a lot less dramatic (and traumatic).

When I visit my Mum in Coatbridge these days, we have a few rituals in place. One of them is to arrange a time when we can align our camera-enabled devices with those of her scattered grandweans, a decent wifi signal at both ends, in order that tough love can be administered live and direct to both Essex and Zuid-Holland. (Kids: no one said the future was going to be easy.)

Add to that the little blue dots that announce the appearance of “family and friends” on your social networks, often buzzing their presence in your coat pocket. Tech can make it seem as if family life was the same mix of jokes, advice, gossip, help, consolation and inspiration as it ever was. It’s now just scattered across the touchscreens of the diaspora.

In the early 50s of Brooklyn, rivers of hot tears flow as precious missives are read and re-read in dimly-lit digs. These days, a few lengthy blethers on Skype would surely sort most of that out.

But maybe not so easily. With his usual eloquence, Colm Toibin recently reflected on his heroine in Brooklyn experiencing both “the easy familiarity of home, and the hard-won familiarity of away”. The wise parent knows that the second kind is to be deeply respected.

Indeed, one of the great joys of social media – if your child is gracious enough to “friend” you – is the way it can show the narrative of the person they are becoming, out there on their travels and travails. And how interestingly unlike you that person is.

Brooklyn is masterful in the way that it uses costume – and the amazing emotional weather-system of Saoirse Ronan’s face – to show the steady victories that comprise Eilis’s “hard-won familiarity of away”.

On her sudden return home, Eilis blazes down the high street of her home village Enniscorthy, wearing populuxe sunshades and a bright yellow dress. These are the fruits of knuckling down to a retail day job in Manhattan, doing night classes in accountancy school, and keeping a puppyish Italian-American boyfriend in her thrall. I doubt the parental challenge of the return of the prodigal child is much different these days. You want them to turn up – whenever they do – and to surprise, even shock you with all the living they’re evidently doing, all the choices they make (and the consequences they take).

You’re glad to have them home, for a while – but you’re also glad they’re not fully at home, even when they’re here. You want them to be restless, to contain multitudes. Surely that’s “job done”?

It’s also hard not to watch Brooklyn with Irish modern history, and recent Scottish political events, in mind. The hard-scrabble poverty of the post-war Irish economy – and the stranglehold of Catholic morality – are very clearly identified as the great drivers of mass emigration.

Now, you’ll know very well the standard trope of Scottish nationalist discourse. We want full powers for our nation, in order that we can create opportunities and prosperity here – meaning that our young people don’t have to emigrate to find fulfilling, decently-paid jobs and prospects.

I vote Yes, but… We’ll need to sophisticate this trope a little – and under pressure from two directions. Firstly, Scotland will become a nation composed mostly of migrants to its shores, just like every other nation in the Northern Hemisphere. The pressures pushing populations up towards us from the South – the resource crises caused by global warming, the wars and strife consequent upon that – are massive and irresistible.

Even within its own genre of Irish-American movies – think of Scorsese’s Gangs of New York, or Jim Sheridan’s In America – Brooklyn shows the gentler face of ethnic assimilation. In the Scottish near-to-mid term, the reality of mass immigration will not proceed with the same cinematic soft-focus. Scots will need to exert their imagination and empathy towards the experience of the migrant as strenuously as they are able.

But, secondly, even if we did strengthen the country through more and better self-government, would it be fair to expect young Scots to only, or even mostly, stick around at home for too long?

What about the glow on Eilis’s face, when she finally masters her sidewalk strut on a commute through Manhattan? What about the joys of not quite knowing where “home” is?

The ideal scenario is, of course, an independence that would compel Scotland to push its best and brightest out to every corner of the world; to trade and connect, tell our story, make friends and relations. An ambitious domestic base that would also require a global schedule; a diaspora that becomes a healthy loop between “home” and “away”.

A situation, perhaps, not unlike that of booming Ireland, in the decades long after the tough 40s and 50s, where the powers of state were adroitly used to modernise and globalise the country (with obvious flaws in the strategy’s latter stages), and reverse those decades of migration.

But let’s remember – as if we could forget – that Scotland still has to truly begin that stage in its national history. No matter how sepia-tinted and poignant the Ireland depicted in Brooklyn, you watch it knowing that their society has a different engine under the bonnet.

We watch them struggle to master themselves, in the early years of their sovereignty. We’ve yet to even properly start.

Brooklyn (12A), starring Saoirse Ronan and directed by John Crowley, is in cinemas now. Pat Kane is a writer and musician (