# Why does moving through time not require energy?

Moving through the other three dimensions necessitates energy. But why doesn't moving through time necessitate energy?

• Who says it doesn't? Compare $E=mc^2$ to $E=\frac{1}{2}mv^2$. I've heard it suggested that $mc^2$ can be interpreted as a kind of 'temporal kinetic energy'. – lemon Apr 17 '15 at 9:35
• The premise of your question is incorrect. Moving does not require energy. Newton's 1st law. – OrangeDog Apr 17 '15 at 10:30
• @OrangeDog that was my first thought as well, but I suppose the question is unclear about whether it's saying a moving body has energy (which is true) or expends energy (which is false). – David Z Apr 17 '15 at 11:05
• What does "moving through time" even mean? Motion of something means that something changes with time. That time changes with time is a tautology. – ACuriousMind Apr 17 '15 at 12:39
• According to Newton's law's your first statement is false. Unless you mean is has to 'have' energy (as opposed to expending it). But since we are all in relative energy frameworks, the question is drifting towards the "Not Even Wrong" area, which is not a great place.... – Jiminion Apr 17 '15 at 13:27

Moving through space at a uniform pace does not require energy, or force (Newton's 1. law), but accelerating through space does (Newton's 2. law). Similarly, moving through time at a uniform pace does not require a force, but if you're accelerating, your time will change wrt. a non-accelerating observer, so in a way you might say that you accelerate through time.

For instance, if you throw yourself in a black hole, free-falling toward the horizon, your time will pass "normally". But when your realize your mistake and use your jetpack to accelerate up of the potential well, back to civilization, you will find that what took ten minutes for you, took 100 years at Earth, so you have increased your speed through time.

• It's interesting to point out how spatial motion implies time motion and vice-versa, it would be cool if something allowed us to decouple time and space like spatial dimensions are decoupled, and thus moving in time without move wrt other observers at rest in space wrt us – mattecapu Apr 17 '15 at 12:37
• @mattecapu: that's because space and time are part of spacetime and everything in the universe moves through it at the same speed, c. At one extreme you have light that doesn't move through time but only space (at the speed of light), if you don't move through space you move through time at c, then there is everything in between but the sum of the two movements is always c – Thomas Bonini Apr 17 '15 at 17:35
• @mattecapu spatial dimensions aren't decoupled. It just seems that way when you're in the middle of nowhere and not moving (like we are) – Jim Apr 17 '15 at 19:00
• @acuriousjim whereas? – mattecapu Apr 17 '15 at 19:34
• @mattecapu for a rotating black hole, you also get the same effect outside the event horizon in the ergosphere, where all motion invariably takes you on a tangential path around the black hole with its rotation – Jim Apr 18 '15 at 14:20

Moving through the other three dimensions necessitates energy. But why doesn't moving through time necessitate energy?

Like OrangeDog and peta said, it doesn't take any energy to move through space. The Earth is moving through space, but it isn't consuming any energy. And like what ACuriousMind said, moving through time doesn't make much sense. To be blunt, it's just a figure of speech that people have grown overly accustomed to. You don't really move through time. When you suffer time dilation it's like you're in slow-motion mode, that's all. An extreme example of this is offered by the stasis box. Like time travel, it's science fiction, but IMHO it gets to the heart of the matter. No motion of any kind occurs in the stasis box. Light doesn't move, electrochemical signals don't move, nothing moves. So when I shut you inside the stasis box for five years then open the door, you think I opened it immediately. You "travelled to the future" by not moving at all while everything else did.

• The description of the stasis box seems contradictory. I would experience travelling into the future because I'm moving very quickly, not because I am frozen in stasis. How is this analogy supposed to apply here? – James Watkins Apr 18 '15 at 16:49
• You don't actually experience any travelling into the future, that's just the figure of speech. You experience less elapsed time on your fast out-and-back trip because your "local" motion is reduced by your macroscopic motion, because the total motion is limited to c. See the simple inference of time dilation due to relative velocity. Imagine watching the light beam whilst panning to follow the traveller. The faster the horizontal motion, the slower the up and down local motion. – John Duffield Apr 19 '15 at 10:50
• Correct, "travelling into the future" is a figure of speech, describing an experience and not a physical phenomena. Your comment on "total motion is limited to c" is really the answer here. You need to elaborate on this and provide an answer in terms of motion. – James Watkins Apr 19 '15 at 14:27

Velocity is defined as distance over time, so based on that premise, you are moving through time at the rate of 1 hour per hour, or 1 minute per minute, or 1 second per second. You cannot go faster than 1 hour per hour relative to your own "clock". You are simply experiencing the one-directional "arrow of time" (Sean Carroll), whereas in space you have a choice in which direction to go. If you are moving through space, you inevitably progress through time.

• Not really, no. – Lightness Races in Orbit Apr 17 '15 at 18:06
• PSA: Don't flag answers you disagree wtih - this is an attempt to answer the question, and will hence not be deleted. – ACuriousMind Apr 17 '15 at 22:23

I am going to interpret your question as, it takes energy to accelerate, decelerate, and overcome friction in the other 3 dimensions, why does moving through time not require energy?

The answer is very simple. In the case of moving with respect to the 3 spatial dimensions - you move. For the case of the time dimension, time "moves" with respect to you!
An example might make this clear. If you sit still and watch a clock, you spend no energy, but you are "moving" though time (time moving through you, would be more accurate).