Einstein’s equations have withstood every experimental test for more than a century. However, according to one philosopher, they have not withstood careful scrutiny of the language used to describe them.
Daryl Janzen, an astronomer and instructor at the University of Saskatchewan, recently published a philosophical challenge in The Conversation. Janzen’s critique does not question the mathematics but instead focuses on how physicists and philosophers describe the nature of space-time itself. He argues that over the past century, the language used to describe space-time has gradually merged two separate concepts into one.
Existence vs. Occurrence
The main focus of this argument is the idea of the “block universe.” In this view, also known as eternalism, space-time is a fixed, four-dimensional structure. All past, present, and future events are equally real within this block, according to this interpretation. Time does not flow, and there is no single present moment. The block contains everything that has ever occurred.
Janzen does not object to the geometry itself. His concern lies with the way the word “exists” is used in this context.
Janzen distinguishes between existence and occurrence. Objects exist because they endure through time. Events occur at a specific place and moment, and then they are over. For example, an elephant standing in a room exists. A cross-sectional snapshot of that elephant, representing a single instant removed from its timeline and frozen in place, does not exist in the same way; it only occurs.
In the block universe model, space-time holds every moment of the elephant’s existence as a four-dimensional world line. This world line shows the animal’s full path through space and time. A single cross-section, or one slice of that path, is not the elephant itself; it is only a record of what the elephant was doing at a certain moment. Janzen says the block is better understood as a representational framework rather than a physical object in the usual sense.
A Problem of When
This confusion leads to a fundamental problem. The entire block universe is said to exist, but it is unclear when it exists. A timeless structure that never unfolds cannot endure as the elephant endures from moment to moment. Meanwhile, if the whole block occurs at once, like a single flash, there is no internal experience of time that could be considered an illusion.
To keep the sense of time passing in a block universe, the four-dimensional structure would need to endure in some sense. This would mean adding a fifth dimension, a second time axis outside the block, for the block itself to exist within; however, this extra axis is not part of Einstein’s original theory.
Janzen uses a simpler analogy. He compares the situation to describing a song that exists all at once, complete but unperformed. A song only becomes a song when it unfolds over time.
Austrian-British philosopher Ludwig Wittgenstein warned that philosophical problems arise when “language goes on holiday.” Janzen argues that physics has been in this situation for decades, reusing words such as “timeless,” “exist,” and “become” in technical senses without considering their everyday connotations.
Implications for Physics and Philosophy
One of the biggest unsolved problems in physics is how to bring together general relativity, which explains gravity and the large-scale universe, with quantum mechanics, which describes matter at the smallest scales. These two frameworks do not fit together, and every real attempt to unify them demands a clear definition of what space-time actually is.
If the language physicists use to describe space-time has been internally inconsistent for more than a century, Janzen suggests the resulting confusion may extend beyond philosophy. Clarifying what physicists mean when they talk about space-time could influence how researchers think about attempts to reconcile general relativity and quantum mechanics.
Janzen does not propose a replacement for the current framework but instead suggests that the fundamental question is not how space-time curves, but how to properly define them in the first place.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.