Why can't we remember the future?: Special relativity, spacetime, and freewill

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First published on 3rd May 2011. Last updated 11 August 2018 by Dr Helen Klus

It may seem obvious that we can't remember the future because it hasn't happened yet, but this cannot be all there is to it[1].

Time can be thought of in two ways: either it's something that flows as the present moves away from the past and towards the future, or it's something that is static, the past is just as real as the future, and our experience of the present is an illusion. The former idea is known as the tensed theory of time, and the latter is known as the tenseless theory of time[2a].

The tensed theory is the most natural way to think of time and, if this theory is correct, then we are right to conclude that we can't remember the future because it hasn't happened yet. The problem is, there's no physical theory that requires time to flow, and Einstein's theories of relativity specifically state that the tensed theory of time is incorrect[3][4a].

Special relativity states that two observers that are moving relative to each other must both measure the speed of light to be the same. This means that either of the two properties that movement relies on - space or time - must differ between observers. The first consequence of this is known as the relativity of simultaneity. This shows that the concept of the present is relative because events that appear simultaneous in one reference frame may not do so in another.

Einstein described his theory of general relativity as taking "away the last remnants of physical objectivity from space and time"[4b]. This is because a number of different coordinate systems can be used to map the universe, all giving the same results. There is no way to know which system is 'correct' and so there is no absolute system, or prior geometry to the universe[4c][5].

According to Einstein's theories of relativity, space and time cannot exist independently, and so are best thought of as a single entity known as spacetime[6]. Since there can be no time without space, there's no such thing as time outside of the universe, and therefore nothing to measure the flow of time against. If there's no such thing as the flow of time, then all times are equally real, and the universe can be thought of as a complete and unchanging 'block' of four-dimensional spacetime.

Given that the tenseless theory of time is correct, and that the future is as real as the past, then it makes sense to ask why we can't we remember the future. This is not the first time that a scientific theory has contradicted our common sense view of the world. The idea that the Earth orbits the Sun at a 100,000 km/h contradicts the common sense view that we should all fall off something that is moving so fast, and it can be argued that quantum mechanics conflicts with the common sense view that there is only one reality[7].

It's natural to think that time flows from the past to the future, as this is how we understand cause and effect to work, however on a microscopic level all physical processes would still make sense if time were reversed[8]. Some have considered whether we could have evolved to experience the flow of time because it provides an evolutionary advantage[2b]. If this were true, then our brains could have developed the ability to only remember the past in order to create this illusion.

The illusion of the flow of time may have evolved to mimic the thermodynamic arrow of time, which is defined by the law of entropy, also known as the second law of thermodynamics[9]. This states that a closed system will become increasingly disordered over time, assuming that its components move in a random way. Despite what the name suggests, it's not an unbreakable law but a statistical principle. A state of order may randomly arise from a state of chaos, it's just extremely unlikely.

If the flow of time is an illusion, then it may be possible that creatures have evolved to experience time flowing backwards, to remember the future, or even to experience the world without the concept of the present. Some propose that this is not possible because knowledge of the future can create a paradox[10].

Others worry that this contradicts free will[11]. This problem occurs even without the tenseless view of time, however. The behaviour of people is entirely predictable in theory since our decisions are correlated with neuronal assemblies that are large enough to be described classically[12] and many neurophysiologists have confirmed that human behaviour can be predicted[13].

Determinism may not be incompatible with free will because the two concepts are not mutually exclusive. Philosopher Alfred Jules Ayer suggested that free will should be contrasted with constraint, not determinism in 1954[14].


  1. Einstein, A., 1955, 'Letter to the family of Michele Besso, after learning of his death', quoted in Dyson, F. J., 1979, 'Disturbing the Universe', Basic Books.

  2. (a, b) Le Poidevin, R., 'The Experience and Perception of Time', Stanford Encyclopedia of Philosophy, last accessed 01-06-17.

  3. Einstein, A., 1905, 'On the electrodynamics of moving bodies', Annalen der Physik, 17, pp.891-921, reprinted in 'The principle of relativity; original papers', 1920, The University of Calcutta.

  4. (a, b, c) Einstein, A., 1916, 'The foundation of the generalised theory of relativity', Annalen der Physik, 354, pp.769-822, reprinted in 'The principle of relativity; original papers', 1920, The University of Calcutta.

  5. Norton, J. D., 'The Hole Argument', Stanford Encyclopedia of Philosophy, last accessed 01-06-17.

  6. Minkowski, H., 1920 (1908), 'The Fundamental Equations for Electromagnetic Processes in Moving Bodies' in 'The Principle of Relativity: A Collection of Original Memoirs on the Special and General Theory of Relativity', Courier Corporation.

  7. Everett, H., III, 1957, ''Relative State' Formulation of Quantum Mechanics', Reviews of Modern Physics, 29, pp.454.

  8. Wigner, E., 1932, 'Über die Operation der Zeitumkehr in der Quantenmechanik' ('About the operation of time reversal in quantum mechanics'), Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, 1932, pp.546-559.

  9. Carnot, S., 1986 (1824), 'Reflections on the Motive Power of Fire and on Machines Fitted to develop that Power', Manchester University Press.

  10. Smith, W. J., 1985, 'Time travel and backward causation', Cogito. An International Journal for Philosophy, Society and Politics Quezon City, 3, pp.57-67.

  11. Smith, N. J. J., 'Time Travel', Stanford Encyclopedia of Philosophy, last accessed 01-06-17.

  12. Atmanspacher, H., 'Quantum Approaches to Consciousness', Stanford Encyclopedia of Philosophy, last accessed 01-06-17.

  13. Soon, C. S., Brass, M., Heinze, H. J., and Haynes, J. D., 2008, 'Unconscious determinants of free decisions in the human brain', , Nature neuroscience, 11, pp.543-545.

  14. Ayer, A. J. and Pereboom, D. (ed), 2009 (1997), 'Freedom and Necessity' in 'Free Will', Hackett Publishing.

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