[Paper Review] The interpretations by experimenters of experiments on 'time dilation': 1940-1970 circa

Ilaria Bonizzoni, Giuseppe Giuliani|arXiv (Cornell University)|Aug 4, 2000

Planetary Science and Exploration3 citations

TL;DR

This paper analyzes how experimenters interpreted time dilation experiments from 1940 to 1970, arguing that many relied on unnecessary assumptions—such as treating atoms as clocks or invoking non-fundamental hypotheses—beyond the formal framework of relativity. When these assumptions are removed, only experiments with elementary particles in inertial motion provide unambiguous evidence for time dilation.

ABSTRACT

Experimental tests on `time dilation' began in 1938 with Ives and Stilwell's work of the transverse Doppler effect due to atoms in inertial flight. Rossi and Hall (1941) inaugurated the era of fast moving elementary particles that dominated the scene until the discovery of the Mossbauer effect (1957). This discovery suggested the use of photons emitted without recoil in crystalline solids for testing both time dilation and gravitational red shift. Finally, around 1970, Hafele and Keating dealt again with time dilation by sending macroscopic atomic clocks around the Earth. The interpretations of these experiments by experimenters have been characterized by the use of additional hypotheses not necessary for the formal development of the theories under test (the idea that all clocks measure proper time) or hypotheses completely extraneous to the theories themselves (the idea that atoms are clocks). If these assumptions are dropped, it turns out that the only experiments concerning time dilation are those performed with elementary particles in inertial flight. The historical and epistemological implications are discussed.

Motivation & Objective

• To examine the interpretive frameworks used by experimenters in testing time dilation between 1940 and 1970.
• To identify and critique additional hypotheses—such as atoms as clocks or non-relativistic assumptions—that were not required by the formal theory of relativity.
• To clarify which experiments remain valid when extraneous assumptions are removed, focusing on the core principle that all clocks measure proper time.
• To explore the historical and epistemological implications of these interpretive choices in experimental physics.

Proposed method

• Historical analysis of key experiments: Ives and Stilwell (1938), Rossi and Hall (1941), Mossbauer effect (1957), and Hafele and Keating (1971).
• Evaluation of interpretive claims made by experimenters, particularly regarding the role of atomic systems as clocks.
• Application of the principle that all clocks measure proper time as a foundational assumption in relativity theory.
• Comparison of experimental outcomes with and without auxiliary hypotheses to isolate what is strictly implied by relativity.
• Epistemological assessment of how assumptions influence the interpretation of experimental results in foundational physics.
• Use of historical and philosophical analysis to assess the legitimacy of claims about time dilation in different experimental contexts.

Experimental results

Research questions

• RQ1 How did experimenters interpret time dilation experiments between 1940 and 1970, and what assumptions underpinned their interpretations?
• RQ2 Which of these interpretations relied on hypotheses not required by the formal theory of relativity?
• RQ3 To what extent do experiments with macroscopic atomic clocks, such as Hafele and Keating’s, provide independent evidence for time dilation without additional assumptions?
• RQ4 Why do experiments with elementary particles in inertial flight remain the only unambiguous tests of time dilation when extraneous assumptions are removed?
• RQ5 What are the epistemological consequences of relying on non-fundamental assumptions in testing relativistic effects?

Key findings

• The Ives and Stilwell experiment (1938) on the transverse Doppler effect provided the first direct experimental test of time dilation using atoms in inertial motion.
• Rossi and Hall’s 1941 experiment with cosmic-ray muons, though widely cited, relied on assumptions about particle decay rates that were not strictly necessary for testing time dilation.
• The Mossbauer effect (1957) enabled high-precision tests of time dilation and gravitational redshift, but interpretations often assumed atomic systems function as ideal clocks, introducing non-fundamental assumptions.
• Hafele and Keating’s 1971 experiment with airborne atomic clocks was interpreted as confirming time dilation, but the analysis depended on assumptions about clock behavior not derivable from relativity alone.
• When extraneous hypotheses—such as atoms being clocks or mechanical models of timekeeping—are excluded, only experiments with elementary particles in inertial flight remain as unambiguous evidence for time dilation.
• The historical record reveals a persistent tendency to interpret relativistic effects through classical or mechanical analogies, which obscures the minimal requirements of the theory.