In my questions on gravity, I've come to the understanding that spacetime is really just time, and there is no need for space. Anything that requires a distance (for example the distance between two massive bodies for gravitation calculations) could just be a function of time. Can anyone show that there is a need for dimensions of space in spacetime?

To further explain what I'm asking. Michelson Morley proved that there is no aether? However, it is also correct that the Gravity B Probe mission Link proved that there is a bending of spacetime out there. So, if you subtract one from the other, it seems to show there is no space in spacetime.

It seems to me that the only thing required for gravity to work is the time dilation caused by a massive body. We talk about the bending of spacetime, as if it is a 4 dimensional thing. We talk about gravitational waves as ripples in spacetime, but are they really only waves in time? We can see time dilation at work. But can we see spacetime dilation? Can you show me how the dimensions of space are required for gravity?

Here is another way of putting it. There are objects floating around in the universe. The only thing connecting these objects to each other is time, rather than something called spacetime.

I hope that this clarifies the question.


closed as unclear what you're asking by enumaris, rob Oct 22 '18 at 17:23

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 6
    $\begingroup$ Very unclear what you are asking. Maybe somebody could help you if you could explain how you came to realize that spacetime really is just time. As it stands, it sounds as if, when you say "spacetime," you are talking about something completely different from what a physicist means when the physicist says "spacetime." $\endgroup$ – Solomon Slow Oct 22 '18 at 16:36
  • $\begingroup$ By using the speed of light, we often do express the distance to an object in units of time (eg: light years). However, all objects are not along a single line. Some objects are in the x direction, some in y, and some in z, or away in a general vector direction (x,y,z). So your notion of "just time" requires time to be a vector $ (t_x , t_y, t_z,) $. Actually it needs a fourth component $t_t$ which is the usual time that passes when we watch the hands of a clock go around. This looks like regular spacetime relabled using light year distances? $\endgroup$ – Gary Godfrey Oct 22 '18 at 18:36
  • 2
    $\begingroup$ @foolishmuse, in my opinion, you're totally missing the point. If I want to uniquely locate an object in space, there are several things that I need to do. 1) Establish a coordinate system (assume Cartesian coordinates for the sake of the argument); 2) specify three coordinates, such as x, y, and z; 3) specify WHEN that object will be at that point. This means that my model is 4 dimensional, and requires 3 space coordinates and one time coordinate. For lack of a better term, such a 4 dimensional model was given the name "space-time". $\endgroup$ – David White Oct 22 '18 at 19:43
  • 2
    $\begingroup$ @foolishmuse, special relativity has already proven that space and time are connected (see hyperphysics.phy-astr.gsu.edu/hbase/Relativ/tdil.html). If you maintain that time is "real", and you maintain that special relativity is "real", then you should also maintain that space-time is "real". $\endgroup$ – David White Oct 22 '18 at 20:26
  • 1
    $\begingroup$ "what we call spacetime is actually a 4D global time continuum" That does not work as I explained in my answer below. 4D global time continuum would be a signature of (----), which is incompatible with observation. $\endgroup$ – Dale Oct 23 '18 at 16:39

Certainly there is a need for dimensions of space in spacetime. The signature of spacetime is (-+++). You cannot get that signature with only time which would be (-) or (----) depending on how many dimensions of time you were considering.

The (-) signature would not work since it would forbid any closed curves and we know that there are closed spacelike curves. The (----) signature would also not work since it would allow closed timelike curves in flat spacetime. So we need space to fit with the observed geometry of the universe. Time alone is not sufficient.

  • $\begingroup$ Can you give me an example of where we need space to fit the observed topology of the universe? For example, can the bending of light around a star be explained only by the bending of time, or is bending of space also necessary? Can this be proven mathematically? $\endgroup$ – foolishmuse Oct 24 '18 at 2:15
  • 1
    $\begingroup$ Nothing so exotic is needed. If you walk around your table you wind up back where you started but not back when you started. You can draw loops that are closed in space but not in time. That fact indicates that there is only one dimension of time, but multiple dimensions of space. $\endgroup$ – Dale Oct 24 '18 at 10:53

There are phenomena occurring on same axis (dot product) and orthogonal axis (cross product). If time was the only dimension, then how would orthogonality be possible? You would need at least two dimensions, so at least one dimension of space is necessary.

  • $\begingroup$ I'm not saying that there are not objects at different places in the universe. What I'm asking is, is there anything in between them "space" or is there just "time" in between them? Is gravity really just the bending of time, and not "spacetime"? There is no "space" at all $\endgroup$ – foolishmuse Oct 22 '18 at 16:22
  • 4
    $\begingroup$ @foolishmuse, What is your reason for saying that the space that separates two different events is nothing, but the time that separates them is something? $\endgroup$ – Solomon Slow Oct 22 '18 at 16:39
  • $\begingroup$ @foolishmuse I somewhat understand what you are getting at (for example using light speed as unit of distance), but your question was about "dimensions of space". It would be great if you rephrase your question and re ask. $\endgroup$ – Kenny Kim Oct 22 '18 at 17:17
  • $\begingroup$ @SolomonSlow I've edited the original question. We know that there are gravitational waves, but perhaps these are simply waves in time, rather than spacetime. We can see time dilation at work. Can we see any effect from the space portion? $\endgroup$ – foolishmuse Oct 22 '18 at 18:37
  • $\begingroup$ @foolishmuse "Can we see any effect from the space portion?" Sure, look up LIGO. The distance between freely suspended mirrors changes when a gravitational wave is passing by, which is measured by laser techniques. $\endgroup$ – timm Oct 24 '18 at 7:52

Not the answer you're looking for? Browse other questions tagged or ask your own question.