Time changes depending on speed and gravity. But, how does one measure the speed of time? It is logically measurable, but speed is a unit of distance over time. The speed of time would mean time over time which doesn’t make sense. (To measure the speed of time a timeframe would have to be set as the true timeframe, let’s say that’s just Earth’s current timeframe and ignore complications).
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2$\begingroup$ The rate of increase of time at any given location is one second per second. $\endgroup$– Andrew SteaneCommented Jun 17, 2023 at 14:18
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5 Answers
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Even though it is so important to humans in everyday life it can be surprising to learn that the flow of time doesn't exist in physics. Since it doesn't exist there is no unit in which to measure it. I have explored this and related ideas in What is time, does it flow, and if so what defines its direction? and you might find it interesting to read my answer there.
There is a sense in which we can sometimes define a relative flow of time for example when discussing time dilation in relativity. When calculating an object called the four velocity we encounter quantites such as $dt/d\tau$ where $t$ is coordinate time and $\tau$ is proper time, and this ratio is what we generally call the time dilation. This is a dimensionless number so it does not have any units. But although it's tempting to interpret the ratio as a comparison of flow rates, i.e. differences in the rate at which time flows, the calculation does not involve any concept of time flowing.
answered Dec 29, 2017 at 5:48
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1$\begingroup$ But people talk about time going slower as you approach the speed of light; slower implies lower speed. What would the proper phrasing of this concept be? $\endgroup$ Commented Dec 29, 2017 at 5:53
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1$\begingroup$ @Notchmath: Yes, we do talk use phrases like time going slower and indeed I'm guilty of this myself. It's a convenient shorthand for something rather more complicated. What actually happens is that the two coordinate systems, ours and the moving objects, have been rotated out of alignment so a pure time displacement in our rest frame is a mixture of a time and space displacement in the other frame. $\endgroup$ Commented Dec 29, 2017 at 6:06
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$\begingroup$ @Notchmath Read John's other answer carefully. You can describe that phenomenon by simply saying observers moving relative to one another will measured the differences between the time co-ordinates of pairs of events differently. Notice how, by promoting time to a co-ordinate, you get rid of any talk of its "flowing", so one can indeed describe a great many physical phenomenons without reference to "flow". Certainly, this is true for General Relativity descriptions of the physical world. Whether or not the notion of time "flow" can be banished from all descriptions of physics is a .... $\endgroup$ Commented Dec 29, 2017 at 6:07
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$\begingroup$ For more on this have a look at What is time dilation really? $\endgroup$ Commented Dec 29, 2017 at 6:08
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$\begingroup$ So you could describe it as the angle between space and time? $\endgroup$ Commented Dec 29, 2017 at 6:08
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Time is analogous to distance. Just as the distance between two points depends on the route you follow between them, so does the time between two events depend on the route between them.
The effect of time dilation in SR is that the time between two events that occur in the same place in one frame is always less than the time between the same two events in any other frame in which the events occur at different places. Note that it is the duration that changes, not the rate at which time 'passes'. If the duration is 4s in one frame and 5s in the other it is not because time in the first frame is 'running more slowly'- time runs at the same rate in both frames, but the interval is a second shorter in the first frame.
If I drive directly between two cities, while you take a round-about route, your odometer will show a longer distance than mine- that is because the distance I have travelled is less; it is not because my odometer has slowed down in some way or is measuring longer miles.
Likewise with time. The unit of time in physics is the second. If you follow one route between two events you will count off a number of seconds. If I follow another route between the same events I might count off a different number of seconds. That is not because my seconds are longer or shorter than yours- which is what your question seems to imply; it is because we have taken different paths with different durations.
answered Jun 17, 2023 at 13:08
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There is no speed of time, per se. Time is actually measured from phenomena that repeats itself in a smooth way. So you count the repetitions to know the time. Initially, people counted the rotation of earth on its axis and around the sun to define time. In that way they DEFINED one second to be 1/86400 of one day. i.e. And one day to be 1/365 of one year, and so on.
So they reverse the Frequency actually to get the time. This principle is still the primary way we get time.
Measurement of accurate timekeeping is a very essential to do science. So the rudimentary definition of time based on the rotation of earth around itself or around the sun is outdated now. And has been replaced by using pendulums. But they eventually show errors due to many physical factors. So more accurate timekeeping device came into place e.g. Fountain Clocks. Currently, Cesium Fountain Clocks are the ideal watch, you can say. They shoot extremely slow Cs atoms against the gravity to one meter height and the time it would take comeback to its initial position under the gravity is BY DEFINITION assigned ONE SECOND and in that one second scientists measured radiations emitted by Cs atoms vibrate 9192631770 times.
So there is no speed of time but frequency of time you can say.
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Planck time was created to address smallest fundamental units to existence that current understandings can interpret. PLANCK Time is the quantity of time required for light or EM emission to travel a distance of 1 Planck length in ideal vacuum. Or measured as a time frame of about 5.39x10^ -44 seconds, or 0.00000000000000000000000000000000000000000539 seconds It is fundamentally the smallest increment of time
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You're wrong time has a velocity. It is the same as the speed of light.
If you don’t believe this? After the Big Bang what was created were molecules and the first quasars. They formed without an event horizon because event horizons are compressed ‘time’ surrounding a ‘Dark Matter Star’. The first stars generated space-time and created the universal time field that you mistakenly believe is not moving.
It is actually the energy behind the expansion of the ‘space-time’ universe that you think is the whole universe. In reality, space is the foundation of the universe and the part that doesn’t move (does vibrate). You should really know ’How the (Space Time) Universe works, before you declare your definitions.
Support for space-time being generated by Stars: ever see a black spot on a star? When you look up close you see through to the hot glowing surface. That blackness is a displaced vail of space that energy (photons) warp into space-time. It’s simple when space is static it’s space move it and it becomes time.
Einstein got parts of it right. The faster you move ’space-time’ the slower the movement of the object. Simple translation time slows the higher the velocity. At the speed of light (time) time stops. Exceed it and you’ll revert back into your original state, expand into FTL properties and that’s that…
This information is all fact. The information world you live in knows 4.5% of space-time universe at most. We know 97% in your math.
