1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Time is not the 4th dimension

  1. Apr 29, 2004 #1
    Time is just a way of measuring the velocity of the motion of an object through the 3 real dimensions. In order to go into the future you would have to stop your particles for the desired amount of time (basically cryogenics). Your particles weren't present to have their effect on the future so the outcome would be slightly different than what it would have been. In order to go into the past you would have to reverse the past motion of all other particles in the universe (an exact reverse of physical law that affects everything but you). Going by that logic, I am lead to 'believe' that going into the past is literally impossible, but going into the future isn't very difficult at all. Now, if you are one that believes (I'm not saying I are or aren't) that the mind is immaterial then that still leaves the possibility for mental time travel. Any thoughts would be appreciated.
  2. jcsd
  3. Apr 29, 2004 #2


    User Avatar

    Staff: Mentor

    Time is the 4th dimension. Why? We've defined it that way.
  4. Apr 29, 2004 #3
    In all dreamscapes, the past and future are equally likely pictures. It seems that only during the minimum mental activities of sleep can one moves into the past or into the future. The dangers are recurrent nightmares that go around in circle, repeatedly.
  5. Apr 29, 2004 #4
    Length, width, and depth are real dimensions whether we define them or not. Time is a measurement associated with velocity and position. Time and velocity would still exist in 1 and 2 dimensional space.
  6. Apr 29, 2004 #5
    Remembering the past isn't what I really meant by mentally time traveling. I meant a conscious experience of time traveling. It's my personal belief through observation that dreams don't have any significance to consciousness. They are just a side effect of theta wave sleep. Interestingly enough, during theta wave sleep the brain matches the Schumann resonance.
  7. Apr 29, 2004 #6


    User Avatar

    Staff: Mentor

    What if I choose polar coordinates?
  8. Apr 29, 2004 #7


    User Avatar

    How can velocity exist in one dimensional space? Ther would seem to be nowhere to go!
  9. Apr 29, 2004 #8
    Velocity in 1 dimension space would be constant at the speed of light.

    The photon has no mass, so it can be considered to be dimensionless.
    A photon travelling in a straight line would be moving in a single dimension - forwards.
    Any object larger than a photon would have mass so would require 3 dimensions.

    Our perception of visual objects is through a multitude of photons all moving in their own single dimensional trajectory.

    Time for a photon would the 2nd dimension.
  10. Apr 29, 2004 #9
    Do you really believe that something (an object, a particle, etc) is not fully evolving in 3D? Thus only active in a flatland? Or even dimensionless? Hum.
  11. Apr 29, 2004 #10
    If a photon had mass, and dimensions, then relativity would make it extremely hazadous to stand in front of a flashlight - you wouldn't notice tghe photon's at rest mass, but its relativistic mass would leave a mark.

    Before the Big Bang (assuming it happened) there was a singularity. All the energy of the universe contained in a dimensionless point.

    All matter has dimensions, energy does not.
  12. Apr 29, 2004 #11
    Polar coordinates are a measurement of two dimensions (length/width - latitude/longitude). The surface of the Earth only has two dimensions. If we could easily travel through the inside of the earth we would need to add a third dimension to our polar coordinates.
  13. Apr 29, 2004 #12
    Voltage, amplitude, and wavelength. There's your three dimensions for energy.
  14. Apr 30, 2004 #13


    User Avatar

    Staff: Mentor

    Yes, you can have 3d polar coordinates. My point though, was that polar coordinates are not length, width, and depth. But they still work.
  15. Apr 30, 2004 #14


    User Avatar
    Science Advisor

    But only because the third dimension is already known, right? If you give someone your location in lattitude and longitude, they still don't know where you are unless they know that altitude is assumed to be "ground level". This gives them their third coordinate.

    I pretty much agree with your original post. Most of the time I find it usefull to think of time as simply another word for space. Knowing that speed and direction are the same property seen from two different perspectives, and that speed is a time-like measurement, while direction is a space-like measurement, I can logically deduce that space and time are likewise the same property seen from two different perspectives (even if I can't allways grasp it intuitively).
  16. Apr 30, 2004 #15
    The polar coordinates are length and width. Look at a flat map of the world. The depth is still there but not measured because we live on the surface of the Earth. If we ever start living at the bottom of the sea, then we will add a depth to the polar coordinates.
  17. Apr 30, 2004 #16
    Time is motion through space. Without motion, time does not exist.
  18. Apr 30, 2004 #17
    I think, force is spacetime (combined 3-space and 1-time). This is what Einstein had already shown in his general theory of relativity. He said that the gravity force is the same as the curvature of spacetime.
  19. Apr 30, 2004 #18
    Einstein used the curvature of SpaceTime to explain the force of gravity - Gravity Well.
  20. May 1, 2004 #19
    Wow. OK, let's go over this. If I want to specify an event, I need 4 numbers: latitude, longitude, altitude, and time. Hence four dimensions. Or look at it this way: An object could hardly exist with width and length but no depth; there would literally be no distance between one side and the other! Nor could something exist with length, width, depth, but no duration. It would pop out of existence the same instant it popped into existence! Hence, four dimensions.
  21. May 1, 2004 #20
    Of course time is the fourth dimension...by your logic, it exists no matter whether we define it or not.
  22. May 1, 2004 #21
    A point moving through any of the three dimensions experiences time because it is moving. Time does not exist without motion. If anything, time is a +1 dimension to any existing dimension. In other words, time is a property of a dimension to measure motion in that dimension (it takes time to get from point A to point B on a 1 dimensional line, but if the point doesn't move time doesn't exist for it).

    An object doesn't (not just hardly) exist with width, length, and no depth. 1 and 2 dimensional objects are just abstract concepts.
  23. May 1, 2004 #22
    Time is really the 3n+1 dimension. The 3n is cyclic of 3 space dimensions where n is a positive integer. But when n is a rational number, including fractions, then the 3n dimension of space becomes fractal (fractional dimension).
  24. May 1, 2004 #23
    Alright. I'll go over this in a slightly different way. The Minkowski metric tensor can be displayed as a 4X4 matrix. Hence, four dimensions. Doubting the existence of time as a dimension is doubting SR.
  25. May 1, 2004 #24


    User Avatar
    Science Advisor
    Gold Member

    Let's say I define a set to be made up of four members John, Paul, George and Eric. Doubting that time is a dimension of spacetime is like doubting that Eric is a memebr of this set: completely nonsensical, as Eric is a member of this set by defintion just like time is a dimension in spacetime by definiton. You can dispute the effectiveness of theories which use spacetime continuums if you like, but there's simply no room to argue whether or not time is the fourth dimension of spacetime, as it is by definition.
  26. May 1, 2004 #25
    The other question to ask is why the dimension of time remains 1 dimensional while the space dimension changes.

    SR and GR - space is 3 dim and time is 1 dim.
    Superstring - space is 9 dim and time is 1 dim.
    M-Theory - space is 10 dim and time is 1 dim.

    Time is the 1-dim that makes spacetime 4-dim.
    Time is the 1-dim that makes superstring 10-dim.
    Time is the 1-dim that makes M-Theory 11-dim.

    Time is really one dimensional. Its dimensionality will never change in any physical theory.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook