This post has nothing to do with Amy Winehouse, sadly on the list of great talents who, poorly served by those in their lives, lost their way and died tragically and long before their time. (It’s bad enough when the ravages of life — disease and accident — steal away those with gifts. Losing people to human foibles is a more painful loss.)
The topic here is the Block Universe Hypothesis, which I’m revisiting, so the title kinda grabbed me (and I am a Winehouse fan). I’ve written about the BUH before, but a second debate with the same opponent turned up a few points worth exploring.
So it’s back to basic block (everyone looks good in block?)…
Or do they? If the BUH is true, then poor Amy Winehouse never stood a chance of a different life; the arc of her life was fixed when the block universe was created.
Which seems to demand the question: What, then, is the point of the universe? What is the point of this unwinding sense of «now» we all experience? Why does it seem as though we have free will and make choices?
As I wrote in the first post, the implication is that the entire universe (not just what we see now, but all of it past and distant future) was created all at once.
The opposing view is that the universe is essentially a quantum computer running a simulation (called “Classical Reality”) in real-time; it “knits” reality as it goes. The past is a woven tapestry of histories, the future is yet to be woven, and the «now» we experience is the leading edge of the ongoing calculation of history.
In that reality, Amy Winehouse might have found a better path.
(Because only in an evolving universe is there any shred of hope for genuine free will, and a universe with free will is a lot more interesting.)
The metaphysics of the BUH depend, firstly, on accepting a determined universe. Everything in the BUH has, in some sense, already happened.
Secondly, it depends on how Special Relativity transforms simultaneity between frames in motion relative to each other. The rotation into the apparent future is interpreted as meaning it must already exist.
One problem is that simultaneity can only be established after the fact. It’s meaningless in the moment (because, once again, it’s virtual).
This was apparently a big issue in the debate, so I’d like to explore it in detail. Let’s start with a definition of the word:
virtual: adjective; 1. In effect or essence, if not in fact or reality; imitated, simulated.
The secondary definitions all include some notion of “not in fact or reality” one way or another. To be virtual is to lack reality. To say, under SR, that simultaneity is virtual is to assert that simultaneity isn’t real.
Which is exactly what SR does assert.
In my Special Relativity Series, I spent four posts (see: SR#10, SR#11, SR#12 & SR#13), writing about how we define simultaneity; about what it means to say two events happened simultaneously. I also wrote about it in the Blocking the Universe post. The reader is urged to be familiar with those posts.
Very briefly, then, we define simultaneity by considering how long the light from something takes to reach us and subtracting the time it took light to travel the distance. That tells us when the event happened, relative to us.
A crucial point is that we cannot make this determination until after the light reaches us. It’s only in retrospect we’re able to define events as having happened simultaneously. I can’t over-emphasize the importance of this.
To illustrate that simultaneity is virtual, first consider Alex (Frame A), who is moving at 0.5c from left to right in the diagram:
From Alex’s perspective, the events occur in the order Z⇒Y⇒X. They are not simultaneous as they are in our frame (Figure 1). Note that Alex (and Blair below) are shown from our perspective.
Crucially here, the events are causally separated — they cannot affect each other. That no event causes the others is important because all frames of reference respect causality. If event P causes event Q, all reference frames agree P came before Q. It’s only with causally separated events that we can have differing accounts of their order.
Now consider Blair (Frame B) who is moving (also at 0.5c) from right-to-left:
From Blair’s perspective, the events occur in the order X⇒Y⇒Z. When we move towards something, more distant events seem to shift backwards in time. The greater the distance, the greater the shift.
This is why Blair sees the most distant event, X, as first, while Alex, coming from the opposite direction, sees event Z as first. When we move away from events, this reverses — we’ll define the closer events as having happened first.
(BTW: There’s a nice animation showing this same example on the Wiki Spacetime page.)
One thing to understand about the “surface” of simultaneity is that it’s infinite. Another is that it has the same spatial dimension as the spacetime.
With regard to the latter, a spacetime has N spatial dimensions plus one of time. Our 3D reality is actually a 4D spacetime. Our surface of simultaneity therefore also had three spatial dimensions. (None of time because, by definition, a surface of simultaneity is a single instant of time.)
It’s called a “surface” to make it more generic. In our 2D spacetime diagrams (1 space; 1 time), it’s an infinite one-dimensional line. In more sophisticated (and therefore complicated) 3D spacetime diagrams (2 space; 1 time), it’s an infinite two-dimensional plane of simultaneity — a thin slice of time.
As just mentioned, in our 4D spacetime, it’s a volume of simultaneity, and that volume is infinite. It’s all of space at a given instant.
But now keep in mind that a fundamental tenant of SR is that we can make no statements about distant points. «Now» is strictly local and personal. SR expressly prohibits statements about distant events until their light reaches us.
Motion shifts (transforms) how we will perceive the infinite volume of another frame. Our perception of causally separated events varies depending on our motion. (In other words, it’s virtual.)
So what to make of this spacetime transformation that seems to “rotate” what we define locally as «now» into the apparent future along our line of motion?
As we move, the farther ahead we imagine, the further into the future those locations are. (Note that we have to imagine those distant locations, because their light hasn’t had time to reach us. Our virtual 3D surface of simultaneity includes the entire universe. Further note that locations behind us shift into the past. As we move our simultaneity “rotates” to include both “past” and “future.”)
Simultaneity also shifts further into the future (and the past behind us) the faster we move. At the extreme, light speed, the shift is maximizes such that it matches the travel time. For example, moving at c towards an object one light-year away sees time at the object shift one year into the future. The photon is simultaneous with its arrival time (for all points along its path).
Think about that for a moment. To the photon, all times along its path are simultaneous. What that does that say about just how virtual simultaneity is?
Let’s put this in more concrete terms. Let’s talk about the Andromeda Galaxy (2.537 million LY away) and what happens to simultaneity with a brisk walking speed of 3 m/s (meters per second).
That’s 6.71 MPH. For reference, when I’m walking regularly, my target is 4 MPH (1.79 m/s), which is a reasonable working stride. Usain Bolt was clocked at 27.8 MPH (12.4 m/s). The point is, 3 m/s is easily doable on foot.
I picked 3 m/s because light speed is 300,000,000 m/s, so our velocity as a simple fraction is 1/100,000,000 c. It makes the math a little easier.
But good luck finding any regular calculator capable of giving a result for numbers that small. I had to use my arbitrary precision suite to get an answer I could use:
γ = 1.00000000000000005000000000000000375
Which is very, very close to 1.0, which is gamma (γ) standing still. (I have the value to over 100 digits of precision, and the pattern above continues; a long string of zeros alternated with clumps of other digits.)
I’ll spare you the calculation. What it boils down to is this:
If one trots towards the Andromeda Galaxy at 3 m/s, one shifts «now» there just over 800,000 seconds into the future. That’s about 9.25 days. (If one trots away, the shift is into the past.)
The shift is greater with increased speed. At light speed, it shifts as far as possible, 2.537 million years.
The shift is also greater with increased distance. The CMB photons we see, generated shortly after the universe began, saw Earth, 13.5 billion years into the future, as simultaneous with them when they were created (and ever since).
Many interpret this to mean spacetime must already exist.
But any analysis shows that, firstly, there’s no way to ever leverage such simultaneity (because it’s virtual), and, secondly, it can’t even be demonstrated. So it becomes a metaphysical interpretation.
Let’s think about the Andromeda and Milky Way galaxies. I think it’s a safe assumption that the particles involved in both — compared to far more distant particles — have roughly shared a broad fuzzy “world tube” since the Big Bang.
The diagram above shows the Milky Way and Andromeda galaxies since the Big Bang when their particles were created. We can access our own past up to «now», but we only have access to the Andromeda galaxy up to about 2.5 million years ago. (Light rays from point X have had time to reach us.)
Because the particles in both galaxies have evolved in roughly the same reference frame, we can assume there is a current «now» in Andromeda, but any knowledge of such is 2.5 million years in our future. (For all we know, Andromeda vanished 2.4 million years ago and isn’t there «now».)
In fact, the area marked as “unknown!” should extend from point X forward. (I just wanted to make the point we are forbidden — by Special Relativity — from making definite statements about «now» in Andromeda.
Photons emitted now from the Milky Way and headed towards Andromeda (destination point Z) consider Andromeda 2.5 million years from now as simultaneous. But as mentioned, Andromeda may not even be there anymore, so there’s nothing we can say about that future (until another 2.5 million years after it).
More importantly, although we can believe there is a «now» in Andromeda based on reality knitting there as it does here, there is no reason to believe the unknit future exists.
Simultaneity is an after-the-fact assessment of spacetime, and it’s entirely virtual depending on our frame of reference.
Bottom line, one is free to commit to the metaphysics of an evolving universe or a block one. Special Relativity does not require the future to already exist.
Stay unblocked, my friends! Go forth and spread beauty and light.