How can we scientifically measure love? I want to understand the psychology of love, and I found the Triangular Theory of Love on Wikipedia from this question, which I think is very believable. However, there is a big section on mixed support where it only says a little bit about THAT love was measured, not HOW:

&quot;Sternberg measured his theory on couples who were roughly the same age (mean age of 28) and whose relationship duration was roughly the same (4 to 5 years).&quot;
&quot;The two other most obvious problems with Sternberg's theory of love are as follows. The first is a question of the separate nature of the levels of love. The second is a question of the measures that have previously been used to assess the three levels of love.&quot;

Can we scientifically measure love (without just asking the lovers)? How?
One way to measure love is to look at behaviors that people engage in to express love. 

Chapman (1995) theorized that there were five broad classes of behaviors that people would engage in to express love: (1) words of affirmation, (2) spending quality time, (3) giving gifts, (4) acts of service, and (5) physical touch. 

Goff, Goddard, Pointer, and Jackson (2007) developed a survey instrument to measure expressions of love. They created a series of questions that were designed to measure one (and only one) of the different behaviors that Chapman laid out. These involved asking questions about how a lover does things like: "giving presents," "offers encouragement," "spends time with me," "holds my hand," and "does yard work." 

The goal of this work was mainly to see if the Chapman classes of expressions of love matched the kinds of behaviors that people wanted in a lover. The researchers administered the survey to a few hundred people, and in general found that the Chapman classes were a good set of high-level descriptions. People who tended to want one kind of behavior in a lover, e.g., receiving words of affirmation, also wanted other kinds of behavior from that class, e.g., receiving compliments. 

References

Chapman, G.D. (1995). The five love languages: how to express heartfelt commitment to your mate. Chicago, IL: Northfield Publ.

Goff, B. G., Goddard, H. W., Pointer, L., &amp; Jackson, G. B. (2007). Measures of expressions of love. Psychological Reports, 101, 357-360.