Makes me think of this : https://en.m.wikipedia.org/wiki/Terrell_rotation
How when going at relativistic speeds, you start to appear to rotate to obervers even if you are going straight - you can even see behind the object!
How when going at relativistic speeds, you start to appear to rotate to obervers even if you are going straight - you can even see behind the object!
That happens because time is a factor in how light from different parts of the object will reach the observer. Light from its far side takes longer and in that time the object continues to move. You can see behind the object, because its rear end moves out of the way of the light coming from itself during the travel time of that light.
It doesn't need to move as far as the light does.
Thank you, that made it click for me!
It only seems weird to us because our senses and minds evolved in an environment where things we can perceive never differ by relativistic speeds.
Like, how the energy required for an object with mass to approximate the speed of light in spacial dimensions goes to infinity, even though it's already traveling at that speed through spacetime.
Or quantum mechanics.
On the other hand, my understanding is that quantum mechanics is another beast entirely, and one of the biggest problems in physics, and to developing a "theory of everything", is to unify quantum mechanics with general relativity.
But if you are interested, a significant amount of the basics of quantum mechanics follow directly from Fourier transforms -- which unfortunately are harder to self-study than spacetime rotations.
Similarly, only vectors with zero length in the matter direction can have unit length in the space/time direction. This is the “only massless particles move at the speed of light” rule.
Things don't "move through spacetime": https://physics.stackexchange.com/a/133821
Working out all the implications becomes very complex.
But then you probably wouldn't have life to observe it if the simple rules didn't have complex emergent behaviors.
Wouldn't the causality speed limit just cause those gravity interactions to arrive with a time delay rather than being instantaneous?
Which means that to simulate the universe you essentially have to keep a history of how gravity is propagating, which requires keeping more information than if interactions were instantaneous?
In a sense perhaps this applies to light too, because since it has a finite velocity now you have to keep track of how all the photons individually propagate through spacetime, whereas if light traveled instantly this would not be necessary?
EDIT: The advantage I see in a speed limit is that you should be able to compute what happens in a point of spacetime based only on the information that is around that point (which still might have come from any or all other particles in the universe, mind you). For me, this emphasizes how important locality must be and it basically converts the popular "spooky action at a distance" claims into nonsense to me.
I guess that's why I'm a fan of the Many Worlds Interpretation.
Gravity waves also travel at the speed of light.
Since they have a speed limit you have to keep track of all gravity waves associated with all particles of the universe throughout all time and space.
So all particles still interact with all other particles, all the time, it's just that they do it with a time delay.
If there wasn't a speed limit it would be much simpler because all gravity interactions would be instantaneous and you wouldn't have to keep track of gravity waves.
However, since the speed of light is miniscule compared to the size of the universe you can ignore all but the most local interactions, and just schedule a computation sometime in the future when you know that the light vector will interact with something.
While instant calculations would perhaps make for a simpler system conceptually, the speed limit and locality principle ensures that less processing power is needed (at the cost of a lot of memory).
With a effective speed limit to space-time, you can "localize" the computation to the spaces where light has reached. And who knows, maybe light can't travel forever, it might just disappear after crossing some distance we still haven't measured (how we'd do that, who knows).
Giving yet another evidence to the "grand simulation" theory. "The universe" is just a group of simulated worlds connected by interacting photon particles (light).
But my point was that this also makes the universe more complex than an alternative fictional universe where information can be accessed instantaneously across any distance (which still allows for distributed computation, if synchronization or lazy computation is possible).
Some processes that are outside of scope we can sense seems like a too cheap explanation.
But we can deduce from various cues that it is being "simulated".
The Double slit experiment is one, experience of deja-vu another, dreams that partly manifest in reality after some time, the apparent speed limit of light, out of body experiences, the fact we are the only local top intelligent lifeform in this part of galaxy, etc...
All signs of processes and memory "bugging out". Except the last one, that one seems to be by design.
Where are mesoscale "bugs" of cells or the like?
Or is it only on the level of quantum effects and errors of the brain, wherein you're overlaying quantum jargon onto another iconprehensibly complex function?
Nothing, it was just the most obvious example (to me).
And in a physics sense what is an event? An interaction between two things, right? And since there doesn't exist any force that can interact instantaneously across distance, the speed limit of causality is equal to the speed of our fastest forces.
If we discovered some scifi-esque Tachyon particle that traveled at 2C, we could no longer say the speed of light is the speed of causality.
So the speed of light / gravity is essentially the maximum speed of causality, because nothing can travel faster than that.
EDIT: Or you can think in terms of how information propagates through spacetime. In this point of view, the speed of causality is always the speed of light, for everything, including particles with mass.
Mass is what slows the speed of causality for certain particles. For example, while the photons I emit may travel at C, the massive particles that make up 'me' cannot.
Theoretically as I understand it, everything moves at exactly the same speed through space-time, whether it is light, the Earth, etc.
At non-relativistic speeds, this means moving along the time axis at approximately one second per second, with the rest of the movement in space. At relativistic speeds, higher proportions of the “speed” of an object are along the time axis.
As the energy requirements for moving massive objects through space at relativistic speeds are huge, we can only really observe this phenomenon with light, which has no mass, and therefore does not need huge amounts of energy to move through space.
As a result, we call 186k miles per second the “speed of light” when actually it is just the maximum speed anything can travel through space, and due to light being massless, it happens to be the speed that light travels through space too.
Whereas massive particles can remain at rest. There's no such thing as an unmoving photon.
As far as I understand it, having mass is basically a result of moving more slowly through space.
If photons had non-zero mass they could only travel slower than the maximum speed of causality (which would probably be called speed of gravity rather than speed of light, in this alternative universe).
Our evolutionary environment for the most part has excluded relativistic effects.
Though that raises the interesting question of what sense perceptions of an organism evolving under such circumstances might be.
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Notes:
1. Donald Hoffman is the principle proponent of this that I'm aware of: <https://www.quantamagazine.org/the-evolutionary-argument-aga...>. I'm not entirely sold on the hard-line version of his argument; it seems to me that there's a general tendency for adherence to truth to be more parsimonious than outright fabulation, in which the nonessential inaccuracies of the sensing system incur additional costs.