A while ago, I asked: "What is time, t or ct?" The question received responses, but none that fully addressed its conceptual depth. So I am raising it again, not just to press for clarity, but to better understand what is truly going on in modern physics.
Relativity famously dethroned Newton’s notions of absolute time and space, uniting them into the four-dimensional fabric of Minkowski spacetime. Classically, we had the familiar trio of spatial coordinates (x, y, z) with dimension L (length), and time t with dimension T. Simple enough.
But then comes the twist: in relativistic physics, time is replaced by ct, converting its dimension from T into L, the same as space. This substitution is not just for convenience; it is foundational to the geometry of spacetime. So here is the question: if ct is the operative time coordinate, then what exactly is t still doing here?
This dimensional shift emerges from the Lorentz transformations, which demand consistency across spacetime intervals. But once time is scaled by c and dressed as a length coordinate, does t have any physical independence left, or is it just tagging along for old times’ sake?
Consider this: in any inertial frame, an object at rest in space is still said to be moving at the speed of light in the ct direction, a claim baked into spacetime’s structure. Every object, regardless of motion, traces a worldline that keeps pace with light in this four-dimensional sense.
Yet there is a bizarre asymmetry: motion through space generates momentum, inertia, and energy, while motion through time (via ct) seems to carry none. If we are moving at light speed in the time direction, why do not we feel it? Why is this “universal motion” so physically invisible?
It raises a real ontological puzzle: is t just a coordinate label — a projection of proper time, or an echo of Newtonian intuitions — while ct does the actual heavy lifting in spacetime geometry?
Maybe t still matters because it is what clocks measure, experiential time, not coordinate distance. But if that is the case, then is not relativity’s neat geometrization papering over something crucial? Something about the felt passage of time, which ct as a spatial analogue does not quite capture?
If ct is the real coordinate, then what is t, a redundant placeholder, a useful fiction, or a ghost of deeper temporal reality?
https://www.researchgate.net/post/What-is-time-t-or-ct?
Dear Preston Guynn
My question is simple. What is t doing in modern physics if ct has dethroned it? If time is ct what is t?
Dear Ziaedin, excellent question that I´ve developed in some of my papers, especially in "A new interpretation of the special theory of relativity". The clue is that since 1900, Planck proposed that the energy present in 3D is discrete; later, Einstein in 1905 developed this concept into a quantum theory. This presence involves an important time tau, so a faster presence of action "h" involves greater energy (higher frequency). This is the time that must be included in the Lorentz-Einstein equations. So, the 4th dimension is C*tau, and this is the energy's wavelength Lambda. A longitudinal dimension that stays the same; meanwhile, there is no interaction. Not Minkowski time "t", the time of events, or the passage of time. The value of "t" is sensitive to the arbitrary initial time adopted and also to the presence of energy due to Lorentz time dilation, aside from the constant increment of this value due to the evolution of time. With this new understanding of the 4th dimension, now you can understand Poincaré invariance: Delta r^2 + Delta (iCtau)^2 = constant. When Ctau gets a smaller value, that implies a greater energy and also a space contraction, i.e., both smaller values, so the subtraction is constant! It makes sense that physics needs this 4th longitudinal value so the other 3D space can be defined. Values of x, y, and z aren´t sufficient, they need the energy information, and that is what Lambda - C*tau provides! Hope this will inspire you and ResearchGate have all my papers about a novel and a more logical way to interpret relativity and quantum mechanics. Regards
Dear Preston-Guynn and Ziaedin, extending my previous answer to the quantum realm. With this energetic Lambda C*tau you can develop a 4D reality containing all the eigenstates. So, any interaction or observation will involve the projection of this 4D over 3D, i.e., a single eigenstate, and no collapse or measurement problem arises. For example, there is no conflict with a coin with spin up in one face and down on the other; the two antagonistic positions of spin exist not in a unique 2D (same face) but in 3D (coin with two faces separated or a dice with six values, etc.). With the same reasoning, we can deduce that the superposition of eigenstates is in 4D, where each unique state is independent in 3D; therefore, the observation is the projection of the 4D existence over our observable 3D. That model explains why all observation involves only a single eigenstate (no weird collapse or measurement problem); meanwhile, its physical reality in 4D involves multiple solutions. Aristoteles would agree: an entity cannot be "A" and its "Not-A" (orthogonality between the eigenstates) at the same time in the SAME SPACE. No need for trillions of new universes proposed by the many-world interpretation every time a tiny quantum system interacts; just a quantum cluster existing in 4D, where, on an interaction, it will randomly project over 3D. Now, the immediate question is whether this existence in 4D is permanent until an observation or interaction occurs, or if its existence is a fluctuation between 3D and the 4th dimension? The theory of space proposed in 2021 assumes that it is a fluctuating characteristic at the rate of its energetic content, as Planck proposed in 1900 and Einstein clarified it in 1905; the presence of energy in 3D is intermittent (in quanta) and depends only on time (same action "h" presence in 3D with shorter period evidence more energy at 3D). So, the physical presence is an aleatory one-by-one eigenstate scenery. This is the reason why time can't go backwards! It´s impossible to randomly go backwards over the same solution that was randomly present through the passage of time. I recommend this paper: "Philosophy in quantum mechanics novel interpretation supports Einstein´s objection" DOI 10.21275/SR231215193142."
The confusion here stems from conflating coordinate formalism with physical meaning. When you ask what we are "doing with t" if ct is used in spacetime, you're mistaking a unit conversion (multiplying time by c to express it in meters) for a change in physical substance.
Let’s be clear:
t is coordinate time, tied to what clocks measure.
ct is just t scaled to match spatial units in Minkowski geometry.
τ (proper time) is the invariant time experienced by massive particles, the actual "felt" time.
But here's the real kicker: Relativity is not even about time in the Newtonian sense. It's about light... or more precisely, about how photons trace out spacetime structure. The entire formulation is built on how light moves, not how matter "moves through time".
So asking “what is the role of t?” misses the point. What matters is not which coordinate label we prefer, but that everything physical (clocks, decay rates, causality) follows the structure set by lightlike and timelike intervals.
You also mention a “dimensional shift” and a “universal motion” through time, but that is a remnant of Newtonian intuition. Objects do not “move through time” like boats down a river. Their clocks tick because they trace a worldline with a proper time τ, shaped by gravity and motion.
Time is what a clock measures. And a clock does not care whether your equation says t or ct.
Why ct and not vt or ut or wt? That's absurd!
If someone wants to claim that space-time 4 dimensions are (x, y, z, ct) then I want to say that it is completely wrong. The 4 dimensions must be of the same kind. But they are not!
Really scientific understanding of what are really fundamental parameters of everything in Matter “space” and “time” can be, and is, only in framework of the the Shevchenko-Tokarevsky’s really philosophical 2007 “The Information as Absolute” conception, recent version of the basic paper see
https://www.researchgate.net/publication/363645560_The_Information_as_Absolute_-_2022_ed
- where the necessary in this case fundamental phenomena/notions first of all “Matter, “Space”, “Time”, “Energy”, “Information”, which are fundamentally completely transcendent/uncertain/irrational in mainstream physics, and for the posters here, are rigorously scientifically defined.
Including “Space” and “Time” are absolutely fundamental phenomena [“Logos” set elements], which absolutely obligatorily are actualized as concrete spaces, which can have arbitrary number and nomenclature of the “space dimensions”, and fundamentally unique for everything “time dimension”.
In the Shevchenko-Tokarevsky’s Planck scale informational physical model, which is based on the conception, in this case it us enough to tread https://www.researchgate.net/publication/391209088_The_Informational_Conception_and_Basic_Physics it is so explained what is the Matter’s spacetime and why it is as it is:
- in accordance with some of really utmost fundamental in XX century von Weizsäcker and Fredkin-Toffoli findings, Matter is based on a binary reversible logics, and so the ultimate and utmost universal base of Matter is [5]4D dense lattice of primary elementary logical structures – binary reversible fundamental logical elements [FLE] that have [5]4 utmost universal – “kinematical” independent degreases of freedom at changing its state – “FLE binary flip”.
The lattice is placed in the corresponding Matter’s fundamentally absolute, fundamentally flat, fundamentally continuous, and fundamentally “Cartesian”, [5]4D spacetime with metrics (cτ,X,Y,Z,ct), where cτ,X,Y,Z, are 4 space dimensions, ctis the time dimension. FLE “size” and “FLE binary flip time” are Planck length, lP, and Planck time, tP.
The space and the time dimensions compose the Matter’s spacetime above which is fundamentally niohing else than some logical “empty container”, where the all dimensions fundamentally haven’t any specific “own” measures, only relative comparisons of distances in space and events/processes time intervals are possible.
Since Matter is rigorously universally organized system, it is possible to make universal comparisons - “measurements” - of space distances and time intervals using corresponding etalons , say, “meter” and “second”; however , again the etalons can be arbitrary, say, if time intervals are measured by a sand clock, time is measured in, say, kg.
At description and analysis of what exists and happen in Matter, the experimental kinematical parameters data are principally important, and because the FLE flips in all 4space dimensions are identical,
- despite that historically and in everyday humans practice space ∆x intervals, and time ∆tintervals are introduced and measured well differently,
- in physics it turns out to be well convenient to use instead purely only historical time-metrics “t” the metrics “ct ”[c=lP/tP] , since most of formulas become be well more simple and clear, including, say, the Lorentz transformations look in this case as they really are - some applications of Pythagoras theorem, etc. That’s all, and no any mystics. Besides most of the rest fast bodies mechanics [historically the SR] basic formulas are Pythagoras theorem applications as well.
More see the link above, to read series of 6 reDzennn comments June 22, 23, 24, 25, 26,27; 5 ,4 , 4, 1, 5, 3 passages , in comments line [“Load comments” in the article bottom] of phys.orgarticle “New theory proposes time has three dimensions, with space as a secondary effect”
https://phys.org/news/2025-06-theory-dimensions-space-secondary-effect.html it is well useful as well.
Cheers
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