Time does not exist: there is no mysterious substance that would flow everywhere but that one would never see. Time does not flow. Time does not exist alone, time is relation. But space that matters is also relation. It is thus necessary to think time as a non separable way to think space, as relativity theory already implicitly invites us to say. Some consequences of this approach are outlined on a general standpoint and on the point of view of the equations. The difficulty in seizing this point of view puts the mind in front of an epistemological circle, the (provisional) stop of which requires a renouncement of thought: thought is not founded on itself; we cannot avoid sometime to show something of the reality external to thought, and to allot to it some qualities that we are not “sure” of (cf. the postulate of the constancy of light speed). One retrieves the concepts of uncompleteness, uncertainty, undecidable propositions, withdrawal of foundations etc. which are a general characteristic of the contemporary scientific and philosophical thought. Pascal already said in his “Pensées”: “whatever the end at which we were aiming in order to stop and rest, it escapes, slips from our grasp and flees for an eternal run ". But does one think time better today?