Most of us have been on a date where we think we can predict how our time with the person sitting across from us is going to pan out. They’re nice, we think, but we can’t really see it going anywhere serious. We’ll probably just see one another casually for a while before it fizzles out. Maybe it’ll be a summer fling? Whatever – this person is not long-term partner material.

But according to new research, we should give up on the idea that we can accurately foresee where a relationship is going. The study, published in the Journal of Experimental Psychology: General, shows that long-term and short-term relationships are more or less indistinguishable at the outset, making it mighty difficult to tell which dalliances will go the distance and which will fall by the wayside.

“In the beginning, there is no strong evidence that people can tell whether a given relationship will be long-term and serious or short-term and casual,” says Paul Eastwick, an associate professor of psychology at the University of California – Davis and the lead author on the study.

Eastwick and his co-authors surveyed more than 800 people from a wide range of ages for their study, using a state-of-the-art “relationship reconstruction” survey in which people reproduced the events and experiences they had in their previous real-life short- and long-term relationships. 

The researchers asked the participants to reconstruct these relationships from when they first started getting to know the other person, rather than from when they were already in a sexual relationship.

They discovered that romantic interest rises at the same rate in both short-term and long-term relationships. However, at a certain point, romantic interest tends to plateau and decline in short-term relationships (the infamous fizzle). In long-term relationships, in contrast, that romantic interest continues to rise.

Eastwick says it can take a few “weeks or months” for the trajectories of long-term and short-term relationships to “pull apart” and become distinct from one another.

“Some of the most interesting moments in these relationships happen after you meet the person face-to-face, but before anything sexual has happened,” he adds.

“You wonder ‘is this going somewhere?’ or ‘How much am I into this person?’ It is somewhere around this point that short-term and long-term relationships start to diverge, and historically, we have very little data on this particular period of time.”

On average, the divergence in romantic interest begins to occur around the time that the relationship becomes sexual – indicating that sexual compatiablity is a major influence on whether relationships turn into something more serious.

“People would hook up with some partners for the first time and think ‘wow, this is pretty good.’ People tried to turn those experiences into long-term relationships,” Eastwick explains. “Others sparked more of a ‘meh’ reaction. Those were the short-term ones.”

The research appears to challenge the stereotypical idea of short-term relationships as fiery and passionate, while long-term relationships are stable but not particularly sexy. Eastwick’s study instead indicates that dating relationships develop into a longer partnership when a couple is sexually compatible – but run their course faster when there isn’t as much of a sexual spark.

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