30daysoftime
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Day 3: Einstein Made Us A Loaf
When Albert Einstein’s lifelong friend Michele Besso died in March 1955, Einstein wrote a letter to Besso’s family. In it, he wrote one of the most quoted sentences in the philosophy of time:
“People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.”
Einstein died a few weeks later.
What he was pointing at has a name now. The block universe.
The 4D Loaf
The block universe says reality is a four-dimensional structure. Three dimensions of space, one of time, stitched together into a single thing. Every event that ever happened, that’s happening, that ever will happen, all of it exists. Equally real. The Big Bang is over there in one corner of the loaf. The heat death of the universe is at the other end. Your tenth birthday is somewhere in the middle. Your death is somewhere too.
Nothing flows. Time doesn’t pass. The loaf just is.
This sounds insane. It is also where the math points.
Why Physicists Buy It
The argument is special relativity, and once you see it, it’s hard to unsee.
Einstein showed that simultaneity, the idea that two events happen at the same time, depends on how you’re moving. If you and I are at rest with respect to each other, we’ll agree on what’s happening “right now.” But if I get on a train and you stay on the platform, my “now” and your “now” start to disagree. Events you consider simultaneous, I won’t. And not because either of us is wrong. We’re both reading our clocks correctly. The universe just doesn’t have a single shared “now.”
Take that one step further. If my present and your present can disagree, whose present is the real one? Mine? Yours? Some third observer’s? The only answer that doesn’t pick favorites is: all of them. And if all of them are equally real, then the past and future they each describe must also be real, because one observer’s future is another observer’s now.
Philosophers Hilary Putnam and C.W. Rietdijk worked this out in the 1960s. Their argument, roughly: if my “now” overlaps with your “now,” and your “now” overlaps with someone else’s, and that someone else’s “now” overlaps with an event in my future, then by transitivity that future event exists right now. Not metaphorically. Actually exists.
Therefore, if you take special relativity seriously, the future is already here.
“Now” Is Just “Here”
The block universe has a clean way to talk about what feels like flow. “Now” works the same way “here” does.
“Here” doesn’t pick out some metaphysically special location in space. It just means the place I am. Other places are equally real, even though they’re not here. New York exists when I’m in San Francisco. I don’t need to be there for it to be there.
“Now” is the same. The moment I am. Other moments are equally real, even though they’re not now. 1955 exists when I’m in 2026. Einstein doesn’t need to be alive for 1955 to be a real place in the loaf.
This view is called eternalism: past, present, and future, all equally real. It’s the natural ontology of the block universe, and most working physicists, when asked, will admit they think something like this.
The Objection That Doesn’t Go Away
There’s an objection, and it’s the one your gut has been making since the first paragraph.
It doesn’t feel like a block. It feels like time flows. It feels like the present is special, the past is gone, and the future is open. We make choices. We anticipate. We regret. None of that lines up with a frozen 4D loaf where everything is already written.
Philosophers who take this objection seriously are called presentists. They say only the present is real. The past was, the future will be, but right now only this moment exists. This is closer to common sense, but it has a hard time with relativity. If only the present exists, whose present? The presentist owes us an answer, and most of the answers involve denying relativity in ways physicists find suspicious.
For today, the block universe gets to make its argument unopposed.
Rovelli’s Wrinkle
Carlo Rovelli I think mostly buys the block? He doesn’t think there’s a fundamental flow. He’s also not satisfied with leaving it there.
If there’s no flow at the bottom, why does it feel so vividly like there is? His answer is emergence. Flow is real the way temperature is real. There’s no such thing as the temperature of a single atom. Temperature emerges when you have a lot of atoms, statistics, and a viewer who’s coarse-grained enough to perceive averages instead of individual particles. Time’s flow, in Rovelli’s view, is similar. It emerges from entropy, from our memory pointing one way, from our being the particular kind of system we are.
That isn’t an answer that satisfies everyone. The philosopher Tim Maudlin has spent decades arguing that fundamental temporal passage is real, that the block universe view throws away something that ought to stay. I’m sympathetic. But Maudlin is not, today, winning.
So What Does This Mean For Me?
Here is the question that should have been tickling that noggin.
If the block universe is right, if my death is already sitting in the loaf at coordinates I haven’t reached yet, then in what sense am I choosing anything? If my actions tomorrow are already there, written into the geometry, am I just walking down a track that’s been laid?
But that’s tomorrow’s past, sorry, post.
Sources
- Being and Becoming in Modern Physics - Stanford Encyclopedia of Philosophy
- Time - Stanford Encyclopedia of Philosophy
- Rietdijk–Putnam argument - Wikipedia
- Michele Besso - Wikipedia (source for the Einstein letter quote)
- The Order of Time - Wikipedia (Carlo Rovelli, 2018)
- Tim Maudlin - Wikipedia (author of The Metaphysics Within Physics)
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Day 2: A Philosopher Argued Time Doesn't Exist
In 1908, a British philosopher named J.M.E. McTaggart published a paper called “The Unreality of Time.” The argument is exactly what it sounds like. He thought he had proven, with logic, that time is an illusion. Not “feels different than we think.” Not “isn’t fundamental.” Unreal.
Almost 120 years later, people are still arguing about whether he was right. People have written entire dissertations on McTaggart, and yet here I am trying to reduce his paper to a blog post. I’ll do my best to make it make sense.
Most modern philosophers think the argument fails, but the way it fails that matters. McTaggart carved up the conceptual landscape that every philosopher of time has been working in since. If you want to argue about time at all, you’re using his vocabulary, even if you’re trying to refute him.
Two ways to talk about time
McTaggart starts by noticing something obvious once you see it: there are two different ways we order events in time.
The first way is fixed relationships. The Battle of Hastings was earlier than the moon landing. The moon landing was later than the Battle of Hastings. These facts will be true forever. The relationship doesn’t change. He calls this the B-series.
The second way is changing properties. The moon landing used to be in the future. Then it was in the present. Now it’s in the past. The event itself didn’t change, but its tense did. He calls this the A-series.
You use both every day without noticing. “I have a meeting at 3pm” is B-series, it’s at 3pm whether you say it on Monday or next year. “I have a meeting in two hours” is A-series, that statement was true at 1pm and false at 4pm.
So far, no philosophy emergency. Two ways of describing time. Cool.
The argument
McTaggart’s argument has two steps, and the trick is how they trap each other.
Step one: For time to be real, you need change. Stuff has to actually become other stuff. Without change, you don’t have time, you have a frozen catalog of events. Fair enough.
Step two: The B-series can’t give you change. The relationship between Hastings and the moon landing never changes. Nothing in the B-series ever becomes anything else. It’s a static ordering.
So if you want change, you need the A-series. Events have to actually move from future to present to past. That’s where the change lives.
And this is where it gets weird. The A-series is contradictory.
Every event in the A-series has to be past, present, and future at some point. The moon landing was future before 1969, present on July 20, 1969, and is now past. So it has all three properties. But past, present, and future are incompatible. An event can’t be all three.
The obvious response: well, it has those properties at different times. Future first, then present, then past. Not all at once.
McTaggart was ready for that. If you say “at different times,” you’re using time to explain time. You’ve assumed the thing you’re trying to define. The A-series was supposed to be what makes time real, and now you’re using time to fix the A-series. Circular.
So: change requires the A-series. The A-series is contradictory. Therefore no change, therefore no time.
Does it work?
Mostly people think it doesn’t. But the responses split into camps that are still arguing.
Some philosophers say the A-series is real and McTaggart’s contradiction objection is bad. They’re called A-theorists. They argue that having different temporal properties at different times isn’t circular, it’s just what time means.
Others say the B-series is enough, and you don’t need real change in the way McTaggart thought. The “change” we observe is just a feature of how we experience the sequence. They’re called B-theorists. To them, the moon landing being past from where we sit and future from where Buzz Aldrin sat in 1968 are both just facts about a four-dimensional structure that doesn’t itself move.
I’ll get into this in more detail in the next post, while trying to tie it back to Rovelli’s work on time.
Actually, hang on a minute, this is my post.
McTaggart Was Right All Along
He noticed that we use two different vocabularies for time, and we never worked out how they fit together. We just slide between them depending on what we want to say.
That sliding is everywhere once you notice it. “It’s been five minutes.” B-series. “I’ll do it tomorrow.” A-series, scoped to “now.” “I have a 3pm.” B-series. Sometimes in the same sentence, two different ways we think about time.
Rovelli argues that the features we associate with time are emergent. They don’t exist at the subatomic level. Time runs differently in different gravitational fields, which is strange if time is supposed to be a fundamental property of the universe rather than something that arises from how we observe it.
Therefore, time is a human construct, and a British philosopher figured it out in 1908.
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