Can the Future Reach Back and Change the Past?

Can an effect come before its cause?

Imagine you are watching a famous magician. He announces the result of a coin flip before anyone tosses the coin. A moment later, someone flips. Heads. He was right. Over and over, he gets it right. You start to wonder: did the future coin flip somehow make his earlier prediction correct? That is the puzzle of backward causation: the idea that a cause can happen after its effect.

In 1954, philosophers Michael Dummett (1925–2011) and Anthony Flew (1923–2010) started a famous argument about whether backward causation could even make sense. Dummett thought it was at least possible. Flew insisted it involved a logical contradiction — you can’t have an effect before its cause any more than you can have a square circle. For centuries, most thinkers had agreed with David Hume’s simple rule: a cause is the event that happens first. But Dummett forced philosophers to ask a deeper question: must the cause always come first, or is that just a habit of our minds?

That dispute opened the door to a strange and thrilling debate that mixes time, physics, and free will.

The Bilking Argument: Can you always stop the cause?

Max Black (1909–1988) came up with a powerful challenge called the bilking argument. Suppose we believe that a later event (A) causes an earlier event (B). Black pointed out that after (B) happens, we could always step in and prevent (A) from happening. If we do, then (A) never occurs, so it couldn’t have caused (B). Therefore, Black concluded, backward causation is impossible: the supposed effect can always be separated from its cause by a simple intervention.

But later philosophers pushed back. Some said: if backward causation is real, you might always fail when you try to bilk it — your hand might slip, or something may distract you, so the cause still happens. In the magician’s case, if someone tried to stop the coin from being flipped after the prediction, the magician might simply not make a prediction at all, or his behavior would still be correlated with the physical act of holding back the flip. Others argued that even if bilking works in some real situations, that only proves those particular events aren’t causally connected, not that backward causation is impossible across the board. The bilking argument remains a central battlefield.

Time must be a block, not a flowing river

To make sense of a later cause affecting an earlier effect, you need a special picture of time. Most of us think the future isn’t real yet — only the present moment exists. This view is called presentism. If presentism is true, backward causation seems impossible because there’s nothing in the future to do any causing.

So backward causation pushes us toward a different view: eternalism (or the block universe). According to eternalism, past, present, and future all exist together, like every frame of a movie reel sitting on a shelf. The future is just as real as the past. In that world, a future event can causally influence a past event because both exist timelessly.

The debate matters. If the past and future are equally real, then statements about the future already have a truth value today: “You will visit your grandparents tomorrow” is just as true (or false) right now as “You visited them yesterday.” But this idea makes many people uncomfortable. It seems to suggest the future is already fixed, even if we don’t know it yet.

The paradox of killing your younger self

One of the most vivid arguments against backward causation is the consistency paradox. Imagine you have a time machine that sends a signal back, letting you target your younger self. You have a perfect aim, a working weapon, and nothing stopping you — yet you must miss. Why? Because you’re alive today, so you can’t have been killed in the past. But if backward causation gives you the physical ability to kill someone in the past, how can you always fail? This seems like a contradiction.

David Lewis (1941–2001) offered a famous solution. He argued that what you “can” do depends on the facts you take for granted. Relative to your skill and tools, you can hit any target. But relative to the fact that your younger self survived, you cannot kill him. The problem vanishes because the word “can” means different things in different contexts. You can (in one sense) and you cannot (in another). No real paradox.

Still, many philosophers find it spooky that you would always be blocked by something — a shaky hand, a sudden noise, a gust of wind — even though there is no obvious physical law preventing the act. Some recent ideas in quantum mechanics suggest that the laws of nature might “wipe out” actions that would alter an already established future, guaranteeing that the past stays as it was.

Does backward causation take away free will?

If the future is eternally real and backward causation is possible, does that mean we have no free will? At first glance, it seems so. If it’s already true today that you will choose chocolate ice cream tomorrow, then you can’t choose vanilla. Your choice appears forced.

But defenders of eternalism draw a careful distinction between determinism and determinateness. An event is determined if something now makes it necessary (like a law of nature and a prior state). An event is determinate if it simply exists at a future time, regardless of what causes it. The block universe requires only determinateness, not determinism. So even if your future choice is determinate — already part of reality — it can still be your free choice that makes it true. The statement “I will eat chocolate” is true today because you will freely choose chocolate tomorrow; the choice isn’t forced by today’s truth.

Critics reply that a determinate future still seems to leave no alternative possibilities. If the future is fixed, you cannot do otherwise, and that’s what free will requires. The argument mirrors older debates about fate and foreknowledge. In the backward causation discussion, many believe the free will worry can be answered; but the tension remains one of the deepest objections.

Why it still matters: tachyons and quantum whispers

This isn’t just a game for philosophers. In the 1960s, physicists speculated about particles called tachyons that travel faster than light. According to relativity theory, a tachyon moving forward in time for one observer would appear to move backward in time for another. If such particles existed, we might be able to build a device that sends a message into the past. The logic of the bilking argument and the consistency paradox then becomes a real design problem.

In quantum mechanics, some experiments with entangled particles look as if a measurement in the future influences a particle’s behavior in the past. A famous Delayed Choice Quantum Eraser experiment detected a pattern that seemed to depend on what an experimenter did later. However, many physicists argue that the effect doesn’t really involve backward causation — it’s just a mistaken interpretation of quantum superpositions. The physics remains unsettled.

So, can the future reach back and change the past? After nearly seventy years of debate, there is still no agreement. The question forces us to examine what time really is, what causation means, and whether the universe allows genuine freedom. Next time you guess a coin flip correctly, you might wonder: is it just luck, or did something in the future already make up your mind?

Think about it

1. If someone invented a phone that could send a text message to you yesterday, would you want to use it? Why or why not?
2. Suppose a fortune teller can predict your every choice with perfect accuracy. Does that prove your choices are not free, or could you still be choosing freely in a world where the future is already real?
3. Imagine a film where the hero causes an event in the past, but the event had already happened before the hero was born. Is that story impossible, or just hard to think about? What would it take for you to accept or reject it?