Monday, February 4, 2008

Nothing Can Move In Spacetime

Dr. Mark Chu-Carroll, PhD Computer Scientist

Not too long ago, Google software engineer, self-appointed anti-bozo crusader and PhD computer scientist Mark Chu-Carroll (yet another insufferably pompous computer geek, ahahaha…) got terribly offended by my web page Nasty Little Truth About Spacetime Physics. Of course, Mark is offended, not because of my arguments (which went over his head) but because I make fun of a bunch of scientists such as Stephen Hawking, Godel, etc... Mark decided that my problem is that I don’t understand what a dimension is. So, Mark goes into a tirade of outright indignation that is somewhat funny in its own right, especially when, all the while, Mark has half his foot planted squarely in his mouth. Yep, like a bozo.

I really don’t feel like defending myself against Mark’s accusations and crackpottery here simply because I’m tired of it. The fact remains that, Mark’s protestations notwithstanding, time cannot change by definition and, as a result, nothing can move in spacetime. I’ll just repeat a quote from a textbook written by a well-known relativity expert:
There is no dynamics within space-time itself: nothing ever moves therein; nothing happens; nothing changes. [...] In particular, one does not think of particles as "moving through" space-time, or as "following along" their world-lines. Rather, particles are just "in" space-time, once and for all, and the world-line represents, all at once the complete life history of the particle.
From "Relativity from A to B" by Dr. Robert Geroch, U. of Chicago

Obviously I am agreeing with a relativist who happens to understand that nothing can move in spacetime. Yes, there are a few out there. Geroch is not alone but most relativists don’t know this and most, like good old Dr. Mark Chu-Carroll, will refuse to accept it simply because it goes against their chicken-shit Star-Trek time travel religion. Too bad.

Stephen Wells

Stephen (I have no idea who he is) posted an objection to my arguments (comment #33) on Mark’s blog that I would like to respond to, not because Stephen deserves a response, mind you, but because my original rebuttal of that particular objection was inadequate. I’ll revise it in a few days to reflect what I write below. Stephen writes:
Now we move to a 4D spacetime model, where a particle trajectory is in (3+1) dimensions. Louis tries to parametrise all four variables (x,y,z,t) in terms of t, declares that parametrising t in terms of t is wrong (which is true), and decides that all of SR and GR is a massive fraud and conspiracy (which is false).

First of all, it is not true that I decided that all of GR is a massive fraud and conspiracy. I actually believe that GR and SR are useful theories as theories go, even though they don't explain much. I just think that all the nonsense about time travel and the like that Einstein’s followers have been preaching over the last century is just that, nonsense. Relativity does not support time travel and relativity does not prove that absolute motion and position don't exist. In fact, there is every reason to suppose that they do and that it is the relative that is abstract and non-existent. Of course, there is no such thing as a particle trajectory in 4D spacetime but Stephen is not about to concede this little truth. He continues:
Meanwhile, back in the land of the sane, we parametrise a worldline (x,y,z,t) in terms of the proper time tau of the particle along that worldline. So we don't parametrise t in terms of t anyway.
So what? Both delta-tau and and delta-t represent temporal intervals. If anybody thinks that a second time can be used to prove that change can occur in another time, I’ve got a bridge to sell you. If you use tau to show a change in t, you must be prepared to show how tau can change. Why? Because time is time. What’s good for the goose is good for the gander. If t can vary, so can tau. To show a change in tau one would need a meta-tau, and a meta-meta-tau for the meta-tau, ad infinitum. And no, you cannot use t to parameterize tau because that would be circular. The expression dt/dtau does not show that t can change. It is just a ratio of two different temporal intervals measured by two different clocks. That is all. Having wrestled his pathetic little strawman to the ground, Stephen valliantly declares victory:
Louis will never grasp this- he can't allow himself to, after decades spent ranting on the subject. Sad, really.

Sad indeed. Entire generations of young minds believing in a lie. Enough to make a grown man cry. Will I ever get an apology from the likes of Stephen Wells and PhD computer scientist Mark Chu-Carroll? I'm not holding my breath.

See Also:

Why Einstein's Physics Is Crap
How to Falsify Einstein's Physics, For Dummies
Why Space (Distance) Is an Illusion
How Einstein Shot Physics in the Foot
Nasty Little Truth About Spacetime Physics
Physics: The Problem with Motion

15 comments:

ulrich said...

i just wondered what you think about julian barbour's concept of "time capsules". do you think that it's a good concept to "explain" e.g. phenomena related to memory (where time, at least, seems to be a crucial variable)?

Louis Savain said...

Barbour is, of course, correct in thinking that time is not a physical property of the universe. However, he is mistaken in believing that the non-existence of time means that motion cannot exist. It is the other way around. It is the existence of time that would make motion impossible. So his time capsule idea is nonsense, in my opinion. Change does not require a time dimension. Time is an abstract concept derived from change.

Our intuitive understanding of time as a flowing or passing phenomenon has to do with the way the brain records past events and the way it anticipates future events in episodic memory.

ulrich said...

i agree with most you've said. however, i don't think that there is a biological basis (as a kind of mechanism) for our perception of time. i think our experience of time rather results from our capacity to learn via language to indicate or to symbolize certain contingencies. but this experience is linguistically mediated. a prelinguistic child does not perceive time, he only perceives change. therefore it's not possible to anticipate future events (at a biological level). there is only a matching between what we have learnt and the present sense-input. this also means, if there is no matching between the memorized and the present input an incoherence-reaction would follow and the brain(?) is looking for an appropriate response. by the way, i think it is very difficult to communicate about this issues because our common language has a homunculized structure. it would be probably better only to refer to concrete elements and mechanisms. maybe this would avoid to mix up only formalist concepts (e.g. time) and concepts which have an empirical basis (e.g. sense organs, neuronal activations).
to conclude, i think the "illusion of time" has no biological basis (e.g. a certain mechanism), but it is only the result of our capacity to reflect on certain contingencies.

Bob Appleyard said...

Actually have a go at the equations. You make the noises of someone who might understand them. See what happens. It's weirder than you want it to be.

Chris said...

Somebody needs to have a look at unitless time, which is actually commonly used in physics...

Louis Savain said...

I have given up trying to pound sense into time travel crackpots. You guys get no respect from me. You need to kiss my ass. How about that? LOL.

Carl said...

On what basis do you claim proper "time" (tau) is a time? It could just as easily -- indeed far more reasonably -- be called a distance, i.e. the distance along the worldline. Are you fooled by the name proper "time" or by the fact that a symbol suggestive of "t" is being used? The names and symbols mean no more than calling dx "length" and dz "height" or vice versa.

You can certainly parametrize (x,y,z and t) in terms of tau, and it makes as much sense as any parametrization of a line in a 4D space.

Maybe you've got a point buried in that rant, but your language is too sloppy to convey it well.

Carl said...

Ah. Now I understand. You're a programmer. This makes it all clear. For some reason, being a male programmer tends to make one both fascinated by and completely incompetent to comprehend fundamental physics. Perhaps some variety of ADHD or Asperger's. You really ought to study mathematics instead; your personality qualities would produce much more in the way of actual insight.

Louis Savain said...

Carl,

Distance is measured in meters and time is measured in seconds. tau is measured in seconds. Therefore it is time. It's extremely simple. Really. Obviously your advanced knowledge of complex mathematics is preventing you from understanding simple concepts.

PS. I may know programming but I don't consider myself a good programmer. It's probably because I hate it. Indeed, I hate all computer programming languages and operating systems. Heck, I just hate all computers. LOL.

DMG said...

The notion of a fixed, unchanging time dimension in relativity can be thought of as analogous to the idea of fate or destiny.

In this understanding, the statement "nothing moves in spacetime" means "you cannot alter your future." It emphatically does not mean that "you cannot move toward your future."

Fixed spacetime means that a sequence of events is fixed, but entities can indeed move forward from one event to the next. They're just not allowed to go off the 1-directional track laid out ahead of them.

Louis Savain said...

DMG,

Please, give me a break. The expression 'nothing moves in spacetime' means exactly what it says. Nothing means nothing. That is to say, no horses, no cows, no particles, no entities.

Conclusion: spacetime physics is just a pile of BS.

DMG said...

Let me take a different example.

I work in video game design. Our animators use a (simple, Euclidean) form of 4-dimensional spacetime to create the animations and actions of objects and characters in our game.

The animation data they create consists of set of snapshots of the three spatial dimensions of a character/scene at key points along the time dimension, called keyframes. The game engine then interpolates between the keyframes to create an unbroken trajectory for each object or point through spacetime.

We can sample this trajectory at selected time values to show successive frames of motion. Play any game, and you'll see characters' legs and arms move, even though their motion is derived from a 4D spacetime in this way.

What you won't see, however, is the animation itself changing. After the artist has finished perfecting the look of an animation, the keyframes and trajectories don't suddenly change of their own accord. Every time we play a character's walk cycle, it looks exactly the same (high-end games use extra layered animations to make this less obvious to the player). "Nothing moves in an animation file" is the analogous description. This doesn't prevent us from seeing motion, it just means that the motion was set in stone before you ever booted-up the game.

Einsteinian spacetime isn't as rigid as our simplified game animation spacetime, but the same principal applies. By sampling Einsteinian spacetime at intervals along the time dimension (as we do when our brains interpret what we see around us at about 24fps), we see motion - without the underlying spacetime trajectories needing to move at all.

Louis Savain said...

DMG,

At this point, I can tell you that you're wasting my time (pun intended). The idea that Einstein's spacetime is not 100% rigid and unchanging is ludicrous. You cannot sample Einstein's spacetime because you and everything else are in spacetime.

Einstein's spacetime and everything in it does not exist because we actually do observe motion and change. Any physics theory that posits a time dimension is a chicken shit theory.

This is not rocket science, man. Why is it so hard for you and the rest of the Einstein's fanatics to understand?

Natanael said...

You need to be clearer about that you mean that in a static four dimensional spacetime nothing moves *because* that spacetime is *static*.
Don't forget to mention the arrow of time and our perception of "time flow".
If spacetime is a static 4 dimentional space, why do we even experience change/flow of time?
Why do we feel like we are moving across the time axis if spacetime is static?

Abstract comparison: If the formula f(x)=sqrt(x)+x^3 describing the path of a dot (we) is already drawn up as a graph (spacetime), could the dot experience movement across the x axis?

Yes, this is very abstract and probably unprovable stuff.

Shane Murphy said...

Sorry if I'm a bit late here but to save everyone the very confusing conversation I'll explain this time space "theory". Four things einstien talked about were perception, thinking, space and time. His theory was not complicated and I hope scientists didn't fly into space with a watch. What he was saying is that there is no time in space because if you look at space there is no thinking therefore no time. Time exists in thought (past and future). If you watch a car drive past it appears to be moving in time when really the world is one continuous moment. Space is nothing so it does not have time. So although there is no time in form we perceive there to be time and in space there is nothing to perceive. By space I mean the distance between two objects.