# Why isn't time understood to be relative motion? [closed]

1. Summarize the problem

In every way one would observe time, time can be thought of as relative motion. In every way that one would measure time, time is measured by comparing motion. These are falsifiable statements and frustratingly I have yet to find anyone who has been able to correctly falsify them.

1. Provide details and any research

I have researched General Relativity on my own through the internet. I am not a physicist or any kind of scientist, but most of what I have gathered I understood through the three classical tests of General Relativity. And to my understanding all three can be understood by replacing spacetime with time thought of as relative motion. What spacetime then becomes is a mathematical construct.

This brings us to a deeper point, the way in which the time variable is gathered for scientific experiments, and or calculations, or really anyway that the time variable is gathered as put in the first paragraph. Time is always gathered by comparing the motion of something to the motion of another thing. Usually one of these things is an object that moves at a set rate and keeps track of how much it's moved, this is what allows for intelligible calculations to be done with the time variable. So time is actually just a result of motion not a requirement as observed by all observations and measurements of time.

Time dilation is to my understanding at the root of all spacetime phenomenon. To my understanding time dilation can be understood with the idea that mass and energy are more or less equivalent. At greater velocities objects at those velocities require more energy to move because they have more energy and therefore it is like they also have more mass. Does this not explain time dilation without spacetime, if time is to be understood as relative motion? An object that is affected by inertia or gravity is affected by time dilation and this would mean their time or motion relative to other objects, not affected by as great inertia or gravity, would be slowed. Could this not mean spacetime curvature is not actually modeling something physical, but modeling the slowing of motion at a given point in space?

Also let me know if this should go a on different stackechange. I posted a similar question on the physics stackechange and they said it should be put on the philosophy stackexchange.

1. When appropriate, describe what you’ve tried

It also explains the direction of time

Yes, this is something I like about this definition as well. It is nice to find someone who agrees with me on this point.

To my understanding time dilation comes from the warping of space by mass and energy

But if time is just relative motion it can not be a structure that is manipulated by mass and energy, but rather mass and energy are variables that affect an object's motion relative to objects not affected by the same mass or energy. This is what I was trying to say when I said, time is a result of motion not a requirement.

And relativity of simultaneity is the main reason for thinking in terms of "spacetime" rather than just processes happening in time. Finally note that for observers moving at constant velocity, time dilation is symmetrical--I measure your clock to be running slow, you measure mine to be running slow.

Hopefully it is okay to quote the following from this Wikipedia page,

Reciprocity

Given a certain frame of reference, and the "stationary" observer described earlier, if a second observer accompanied the "moving" clock, each of the observers would perceive the other's clock as ticking at a slower rate than their own local clock, due to them both perceiving the other to be the one that is in motion relative to their own stationary frame of reference.

Common sense would dictate that, if the passage of time has slowed for a moving object, said object would observe the external world's time to be correspondingly sped up. Counterintuitively, special relativity predicts the opposite. When two observers are in motion relative to each other, each will measure the other's clock slowing down, in concordance with them being in motion relative to the observer's frame of reference.

While this seems self-contradictory, a similar oddity occurs in everyday life. If two persons A and B observe each other from a distance, B will appear small to A, but at the same time A will appear small to B. Being familiar with the effects of perspective, there is no contradiction or paradox in this situation.

So let's say there is a rocket traveling away from the Earth at half the speed of light. Now obviously the people on Earth would view the people on the rocket as time dilated. But as mentioned not so intuitively the person on the rocket would also view the people on Earth as time dilated. This is similar to the example from the Wikipedia page. The two people standing far apart view each other as small because they are both far apart. This does not mean both people are both actually smaller to one another. Something can't be both one thing and another thing at the same time. This does mean that both people are far apart and from each other's perspective are small. In the rocket example both people are not traveling half the speed of light, but only the people in the rocket. Although from both people's perspective they view each other as separating at the speed of light just as both people far apart view each other as small. Is this not a plausible interpretation using time thought of as relative motion?

Contrarily to velocity time dilation, in which both observers measure the other as aging slower (a reciprocal effect), gravitational time dilation is not reciprocal. This means that with gravitational time dilation both observers agree that the clock nearer the center of the gravitational field is slower in rate, and they agree on the ratio of the difference.

The above is also from the time dilation Wikipedia page and I wanted to make note of it as it appears to agree with the cause of the symmetry of velocity time dilation given above. It agrees because in velocity time dilation from both viewers point view they are separating, but this is not the case with gravitational time dilation, one is simply in a stronger gravitational field and the other is not.

There are two types of time dilation, one due curvature of spacetime by mass/energy in the general theory of relativity, and one just due to relative velocity in the inertial frames of special relativity

Yes, this goes back to what I was saying earlier. Could it be that curvature in spacetime is not the cause of time dilation, but the equivalence of mass and energy is the cause? Is it not true that gravity or inertia increase energy and at greater energy it is as if the object has greater mass and therefore further motion requires more energy to be performed? Would this not mean that compared to objects not experiencing such as great inertia or gravity would be slowed due to the required increase in energy, meaning it's relative motion or time would be slowed relative to the object experiencing a lesser degree of gravity or inertia? Could this not mean that curvature in spacetime is not showing some underlying architecture of the universe, but plotting any given point in space's effect on an object's motion?

I do not quite understand the question. Pretty much anything can be measured by "comparing motion", mass, charge, pressure, frequency, etc. After all, most of physics is just "particles in motion". Not only is the statement too vague to be falsifiable, it is not even clear what "understanding time as relative motion" means.

What is meant by this question is that for some odd reason we humans seem to think there is a past and a future. Many of us can't seem to understand why time only flows in one direction. We question why does cause always precede effect, and it's simple really if just observe. The only time we can really observe is now, why do many of us think that there is some entity containing a past and a future? Why can't there just be now? The past did happen and the future will eventually happen, but that doesn't mean it exists now. It can be predicted, but the future does not yet exist and the past no longer exists. This can be understood by just observing. How does one know time is passing right now? The motion of what makes up one's perception is being compared to what one is perceiving. Memories are being stored in one's brain to form what one knows of the past. Does it not make more sense for time to be understood as relative motion rather than as google would put it,

the indefinite continued progress of existence and events in the past, present, and future regarded as a whole.

That definition is neither observable or falsifiable yet it is regarded as truth and this greatly bothers me. I am not entirely sure if I am the one misunderstanding something or if it is others.

Moreover, how something is measured usually has little to do with what it is, temperature is measured by a height of mercury in thermometers, for example.

But temperature is how fast particles are bouncing around and this is what makes the mercury rise. For instance refrigerators work by compressing a refrigerant. The way in which something is measured can reveal the true nature of what is being measured.

Also are you familiar with the relativity of simultaneity that I mentioned earlier? This principle says that for two observers moving at constant speed, a pair of events at different locations in space can happen "at the same time" in one observer's frame but at "different times" in another's, which shows that at least in terms of testable physics, the notion of an objective "now" doesn't make sense. Like I said, that's one of the biggest reasons to think in terms of 4D spacetime rather than just processes occurring in time.

I am somewhat familiar with relativity of simultaneity and I have used your link to review what I know. To my understanding spacetime is not necessary for understanding what causes this phenomenon and I will use examples from your link to demonstrate.

Relativity of simultaneity

For example, a car crash in London and another in New York appearing to happen at the same time to an observer on Earth, will appear to have occurred at slightly different times to an observer on an airplane flying between London and New York. Furthermore, if the two events cannot be causally connected (i.e. the time between event A and event B is less than the distance between them divided by the speed of light), depending on the state of motion, the crash in London may appear to occur first in a given frame, and the New York crash may appear to occur first in another. However, if the events are causally connected, precedence order is preserved in all frames of reference.

As said by one of the comments, one of the principles that relativity is based upon is that the speed of light is the same for everyone. For instance, if one were in a car moving sixty miles per hour and one were to move their hand forward their hand would move at speed of their hand plus the speed of the car (sixty miles per hour). But if one were to shine a light inside the car the speed of the car would not be added to the light. The light would simply move the speed of light.

So in the car crash example an observer who is not moving relative to the car crashes may view the car crashes happening at the same time, it really just depends on how long it takes the light to reach them. While a plane traveling from one car crash to another will see the one they are closer to or possibly the one they are moving towards happening before the other crash.

The following is picture from Einstein's train thought experiment.

Einstein's version of the experiment[12] presumed that one observer was sitting midway inside a speeding traincar and another was standing on a platform as the train moved past. As measured by the standing observer, the train is struck by two bolts of lightning simultaneously, but at different positions along the axis of train movement (back and front of the train car). In the inertial frame of the standing observer, there are three events which are spatially dislocated, but simultaneous: standing observer facing the moving observer (i.e., the center of the train), lightning striking the front of the train car, and lightning striking the back of the car.

Since the events are placed along the axis of train movement, their time coordinates become projected to different time coordinates in the moving train's inertial frame. Events which occurred at space coordinates in the direction of train movement happen earlier than events at coordinates opposite to the direction of train movement. In the moving train's inertial frame, this means that lightning will strike the front of the train car before the two observers align (face each other).

So lightning strikes a train moving from left to right on both ends at the same time. There is viewer on and in the middle of the train and a viewer on the platform outside the train. The viewer from the outside of the train would view the lightning striking both train ends at the same time because it requires an equal distance from both strikes to reach them. But the viewer on the train is moving with the train to the right and would view the right lightning bolt strike first because it takes less distance for the light of that bolt to reach their eyes. And to clarify the person on the train would view the lightning bolt strike on the right before the person outside the train would see the right lightning bolt strike. Again this because less distance is required for the light from the right lightning bolt to reach person on the train.

Are these not plausible explanations for relativity of simultaneity? And are they not sufficient explanations without the need of spacetime? I can understand that spacetime can be useful for mathematical modeling, but to my understanding it is not what is actually happening.

• I also tend to see time as such. It also explains the direction of time, as the conservation of momentum means one can't reverse a motion's direction without applying force through another motion. To my understanding time dilation comes from the warping of space by mass and energy. Time is compared motion, motion depends on space, thus the notion of spacetime. – armand Jun 7 '20 at 22:16
• Mass/energy equivalence is a separate aspect of special relativity from time dilation, along with length contraction and the relativity of simultaneity (all are derivable from the two fundamental postulates of special relativity). And relativity of simultaneity is the main reason for thinking in terms of "spacetime" rather than just processes happening in time. Finally note that for observers moving at constant velocity, time dilation is symmetrical--I measure your clock to be running slow, you measure mine to be running slow. – Hypnosifl Jun 7 '20 at 22:22
• @armand - There are two types of time dilation, one due curvature of spacetime by mass/energy in the general theory of relativity, and one just due to relative velocity in the inertial frames of special relativity (or 'local' inertial frames on small patches of spacetime in general relativity, where to first order physics should look like special relativity according to the equivalence principle) – Hypnosifl Jun 7 '20 at 22:25
• I do not quite understand the question. Pretty much anything can be measured by "comparing motion", mass, charge, pressure, frequency, etc. After all, most of physics is just "particles in motion". Not only is the statement too vague to be falsifiable, it is not even clear what "understanding time as relative motion" means. Moreover, how something is measured usually has little to do with what it is, temperature is measured by a height of mercury in thermometers, for example. – Conifold Jun 8 '20 at 2:23
• The very philosophy of a "time arrow", and of time being conceived as being a location on par with the spatial dimensions, is highly questionable from a physics perspective. I wrote a question about this some years ago (with extensive further discussion in comments): physics.stackexchange.com/q/387199/179462 – Steve Jun 8 '20 at 18:42