Unblocking the Universe

I think the BU is BS!

Imagine that every bit of it, past, present, and future, exists eternally.

Over time, I have encountered a number of people who believe in the Block Universe (BU) hypothesis. Many of them also believe Einstein believed in it. (For reasons I’ll get to below, I’m dubious.) Perhaps I’m missing an important point, but I’ve never seen the hypothesis as viable. Of course, a metaphysical view is almost impossible to prove or disprove, but I’d be willing to place big money on a bet against the BU. This post is about why.

What is the Block Universe hypothesis?

The conventional view is that the universe began with the Big Bang and has been expanding ever since. In particular, events — specific moments in space and time — are the result of events in previous moments. In Einstein’s unified spacetime picture, each event has a past light cone containing all events that could affect it.

In this view reality is an ongoing computation of matter and energy. A metaphor might be of a large loom weaving the fabric of reality. The present is the leading edge of that fabric. The past is the woven cloth, and the future has yet to been weaved.¹

The Block Universe hypothesis says that all events from the Big Bang onwards already and always exist. All moments in time exist forever. A common metaphor is of a giant block of Lucite with tracks through it representing the 4D “worms” of objects (all matter).

What argues for the Block Universe?

From what I’ve heard, there seem some common arguments in favor of the BU hypothesis:

1. It’s supported by simultaneity in Special Relativity.

2. It’s supported by physical determinism.

3. Einstein said so.

4. It supports reversal of time, which physics supports.

As you’ll see, I think the first is a misunderstanding, the second isn’t true, the third is debatable, and the fourth is probably irrelevant.

What argues against the Block Universe?

I think there are some strong arguments against the BU, and for me they are strong enough to essentially rule it out:

1. What created all that structure and when?

2. How to explain our sense of “now”.

3. Special Relativity denies the reality of “now” except locally.

4. The universe is not deterministic because quantum mechanics.

5. A Block Universe seems to imply a lot of mass.

6. And information. A [x,y,z,t] event for everywhere & everywhen.

7. Einstein said so in a personal letter to the widow of a friend.²

8. Time doesn’t go backwards.

These are semi-ordered by (my perception of) argumentative power. Some of the above (#3, #4, #7, #8) are responses to the arguments for the BU (and #8 is a deep rabbit hole all on its own). The others are points I’ve never heard addressed — at least not satisfactorily — by those arguing in favor of the BU.

Considering the Arguments

Let me start with my two biggest objections (points #1 and #2 above): the BU’s creation story and the experience of past and future divided by the razor edge of “now”.

How did a BU happen?

As point #6 says explicitly (and slightly redundantly), a BU implies that every event in spacetime, for all of time, already exists. What created all that structure? How did it come to be? Did it spring into being instantly? Or was it somehow computed? (If so, how is that different from reality seeming to compute itself as it goes along, as it appears to do?)

There is an unimaginably huge amount of computation implied — an entire universe of computation for all of time. And if it all exists, why do we seem to live in the moment of “now” that apparently is sliding through the Block? Why does the universe seem to unfold for us?³

For me, these alone are enough to argue strongly against the idea. The notion of a dynamic universe weaving itself moment-by-moment (and thus spreading all that computation across space and time) seems far more likely. I can’t really conceive of how a BU could come to be.

There is also point #5. If we measure the mass of something in the present moment, we get the same value as in the past or future. What if someone in the past or future also measures that mass? If all moments exist, does this mean the mass exists in all moments past and future?

If we integrate all the mass over all the Block, we end up with a universe that has unimaginably more mass than the one that appears to us moment-to-moment. So, I think this point alone, also, is a strong argument against.⁴

Special Relativity

Proponents of the BU hypothesis point to how, in Special Relativity, there is a “surface of simultaneity”⁵ that rotates events distant from you into the apparent past and future.

The idea is that if one is in motion relative to distant events, then those events (later!) judged to be happening “right now” turn out to be events in your past or future.⁶ The argument is that the simultaneity of distant future events argues they must eternally exist. And distant past events must continue to exist because they, too, can be (later!!) judged to be “simultaneous”.

The point gets a bit technical (which may be why it’s misunderstood). The bottom line is that Special Relativity explicitly denies the reality of “now” anywhere but in your immediate frame of reference. Any events distant from you can only be judged to have happened simultaneously after their light reaches you. This eliminates the apparent need for these distant events to somehow already and always physically exist.

Our judgement of distant events always comes after the fact.

So, I think this point not only fails to argue for the BU, but SR explicitly says it’s the wrong way to look at it.

If you’re interested in Special Relativity but know little about it, see this series of illustrated posts that try to explain it as simply as possible (but no simpler).

Physical Determinism

Sorry, but it went out the window when quantum mechanics came into the picture.⁷ We now know (contingently) that the universe is random at its lowest level. And many quantum effects do manifest at our macro level (stars shine because of quantum effects — beta decay depends crucially on both the weak force and the Heisenberg Uncertainty principle).

The mathematics of classical physics is indeed fully determined, but in the same way there are no ideal physical circles or squares, I believe the physical world works only in very close approximation to classical physics.

Classical physics is in the same Platonic realm as circles and square (or spheres and cubes). It’s an idealization of what we experience and establish through experiment. But the physical is cruder and — because of this — not actually precisely determined.

I’ll go so far as to opine that physical reality may be governed only by rational numbers, not the idealized Platonic real numbers. And if so, this implies a precision limit on the extent to which the past can determine the future.

Einstein’s Letter

I’m not an Einstein scholar, so I may be wrong, but I’m not aware of anything Einstein wrote professionally that suggests he believed in the BU. He did believe in physical determinism (‘God doesn’t play dice’), but that’s one of the things he turned to be wrong about. God does “roll dem bones”.

The personal letter he wrote was to the family of Michele Besso, a close friend of his. Being who he was, he couldn’t very well offer the usual consolation of the loved one looking down from Heaven, so he offered a notion from physics:

“Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion.”⁸

Which doesn’t seem a particularly strong statement favoring the BU. It can be read as merely a reference to determinism and relativity. Or as just a kindness.

Reversed Time?

This is a deep rabbit hole I’d like to get more into another time. For now, I’ll just say I believe time is both axiomatic and fundamental.⁹

The idea of reversed time comes from how the fundamental laws of physics work the same forwards or backwards. As one example, the reverse of a Feynman diagram describes a valid interaction.¹⁰ This seems, to many, to suggest time could potentially be reversed.

To me, the breaking of glass or eggshells seems to falsify the notion that time can actually run backwards. Even the falling glass of water doesn't have the same physics in reverse. In the one case, a single impulse and forces dissipated piecemeal over an area, in the other, that continuum of forces spread out in perfect synchronization to accomplish the reverse. Not, perhaps, physically impossible, but clearly two distinct situations.

Entropy is certainly a part of that, but beyond entropy it seems to me there are real-world processes that only occur slowly over time — the growth of crystals or eggshells, for instance. No manner of applied forces seems capable of seamlessly fusing broken glass or eggshells.

Winding back determined actions that have already occurred (using -t rather than +t) is just post-diction, not time going backwards in any real sense.

Quantum mechanics and wavefunction reduction likewise make reversed time an impossible notion, but that is grist for another mill.¹¹

Until next time…

1. The metaphor has been reified in both mythology and science fiction. Including, if I recall correctly, an episode of Doctor Who.

2. Also, Einstein wasn’t always right.

3. If the BU was true, it would tell us that we’re moving through time rather than time flowing past us, a long-running metaphysical debate.

4. The only way out would be to argue that mass somehow moves along the moment experienced as “now”, but the Block implies a physically real simultaneity of past, present, and future.

5. In fact, in 3D space (4D Minkowski space), it’s a 3D volume that includes the entire universe.

6. The effect depends on both relative speed and distance. Walking speed is enough to shift events in the Andromeda galaxy by several weeks.

7. If you’ll forgive a mixed metaphor.

8. Often misquoted as: “Reality is merely an illusion, albeit a very persistent one.”

9. It just is, and nothing comprises it.

10. In fact, all 90° rotations of any Feynman diagram describe valid interactions.

11. But you can perhaps see what I mean by a deep rabbit hole.