Martin Heidegger, the most celebrated continental philosopher of the twentieth century, places at the centre of his thoughts the notion of “being in time” - indeed, his magnum opus is called Being and Time (Sein und Zeit). For Heidegger, time was more important to our existence than space. But how should Heidegger's idea be understood in connection with Einstein's theory of spacetime?
The contents of Being and Time are notoriously difficult to appreciate, and doubly so for non-German speakers since Heidegger draws frequently upon grammatical features of his native language that don't always translate into other languages. The centrepiece of his ideas is Dasein (often translated as “being-there”, although Heidegger denied this was accurate). A shorthand for understanding Dasein is that it means the experience of being aware of time, of the consequences and the circumstances of being positioned in a history we can look back upon, and aware of our death ahead of us. We think of this kind of perspective as being uniquely human – while other animals are certainly beings, only humans are Dasein as far as we know. It is vital to Heidegger's idea that Dasein is always already embodied in time – there is no question of considering human consciousness as a separate subject for him. We humans are thrown into time as Dasein, and it is thoroughly fruitless to doubt external reality, we simply must attend to our 'throwness' as it comes.
For the purpose of this discussion, the key point to raise is that for Heidegger time was more important to Dasein than space. Where we are born in the world can become quite irrelevant as we move through our lives, as we can relocate, learn from other cultures and so forth. But we cannot move through time in this way – when we are born is of critical importance both to who we are and whom we can become. If we were born in ancient Greece we could not possibly become an astronaut, for instance, whereas if we were born into an Amazonian tribe we could still potentially become an astronaut (however unlikely) as long as we were born in this time.
A challenge the physicist may want to raise is that this separating out of time and space is misleading, since what we are really existing within is spacetime, a four dimensional continuum in which treating time and space as separate is misleading. But it is the physicist here who is misled – they have mistaken a mathematical model as having precedence over the actual terms of our existence (or our Dasein, in Heidegger's term), mistaking a scientific model as being necessarily of higher importance. It's the same kind of error a theist makes when they mistake their concept of God for truth – one may very well claim that God has access to universal truth, but that does not warrant any claim by the believer in God to any such access; to do so is tantamount to blasphemy in conventional religious terms. The physicist's prioritising of the spacetime model over humanity itself engages in a similar kind of immodesty.
Recall Hannah Arendt's commentary on Heisenberg's notes as to how quantum physics changed our understanding of science: the experiment remains a “question put before nature”, and as such the answers of science always remain questions asked by people. We are confused over what is “objective” when we assume that there can be answers without questions and a question-asking being – a Dasein, in Heidegger's terms. Dasein comes first and it alone is primordial to our experiences and knowledge. Science is a set of tools for thought and action that depend first and foremost upon Dasein, upon our being in time. There can be no science without thinking beings to conduct it.
Spacetime, then, is a tool that can be at hand for us to use as Dasein (in understanding the nature of the universe as we observe it, for instance) but it does not mean that the concept of spacetime is more fundamental than the notion of time in the context of being and existence. We all too frequently mistake our scientific tools for objective truth because the modern paradigms of science trick us into thinking that our experimental results, and the theories that organise these, are meaningful independent of humanity. But this is far from the case: they are a product of our being, our Dasein. Another kind of being would not necessarily derive the same theories. A hypothetical entity whose awareness was embodied within spacetime (rather than time) could not arrive at anything like Einstein's theory of general relativity, which has its sense precisely because space and time are separately measurable for us.
Yet Heidegger may yet have spoken too soon when he said that time was more important to Dasein than space, for this assumption rests securely on the idea that when we talk of spatial separation we are talking solely of distances upon our world. Heidegger never entertained the possibility of sentient beings elsewhere in the universe – of non-terrestrial Dasein. And if this is allowed, then spatial separation could be far more radical than temporality in changing the nature of how Dasein is thrown into the world...
But perhaps we would be wise to heed Daniel Dennett's caution to be wary of science fiction thought experiments, because the strong intuitions they form may be illusory (a warning also hinted at by Wittgenstein). Whether or not there is alien Dasein doesn't matter for us at the moment because there is no question or possibility of our being thrown into their world – we are always already thrown into this one. And for all of us, as Dasein here on Earth at this time, the question of when we live has truly become vastly more important than where.