What is Planck time: Definition and 27 Discussions

In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of four universal physical constants, in such a manner that these physical constants take on the numerical value of 1 when expressed in terms of these units.
Originally proposed in 1899 by German physicist Max Planck, these units are a system of natural units because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one of several systems of natural units, but Planck units are not based on properties of any prototype object or particle (the choice of which is inherently arbitrary), but rather on only the properties of free space. They are relevant in research on unified theories such as quantum gravity.
The term Planck scale refers to quantities of space, time, energy and other units that are similar in magnitude to corresponding Planck units. This region may be characterized by energies of around 1019 GeV, time intervals of around 10−43 s and lengths of around 10−35 m (approximately respectively the energy-equivalent of the Planck mass, the Planck time and the Planck length). At the Planck scale, the predictions of the Standard Model, quantum field theory and general relativity are not expected to apply, and quantum effects of gravity are expected to dominate. The best-known example is represented by the conditions in the first 10−43 seconds of our universe after the Big Bang, approximately 13.8 billion years ago.
The four universal constants that, by definition, have a numeric value 1 when expressed in these units are:

the speed of light in a vacuum, c,
the gravitational constant, G,
the reduced Planck constant, ħ,
the Boltzmann constant, kB.Planck units do not incorporate an electromagnetic dimension. Some authors choose to extend the system to electromagnetism by, for example, adding either the electric constant ε0 or 4πε0 to this list. Similarly, authors choose to use variants of the system that give other numeric values to one or more of the four constants above.

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  1. B

    B Is the highest frequency possible the inverse of Planck time?

    Is the highest frequency possible the inverse of Planck time? Separate or connected question, what's the highest frequency achievable practically today?
  2. R

    B Is There a Connection Between Planck Length and Planck Time in Relativity?

    If Planck length is 10^-35 of a meter and Planck time is 10^-43 of a second, doesn't that mean that as the relative speed gets closer to the speed of light and time acceleration and length contraction are happening, they are happening at a different rate, since length contraction has to reach...
  3. George Keeling

    I Comparing Planck's Mass, Length, Time and Energy

    Sean Carroll gives the Planck's set of four dimensioned quantities: Planck's mass, length, time and energy. I wanted to compare them with actual things.\begin{align} m_p=\sqrt{\frac{\hbar c}{G}}&=2.18\times{10}^{-8}\rm{kg}&\rm{{10}^{7}\ E. coli}\phantom {100000000000000000000}&\phantom...
  4. K

    I Does Planck time violate Lorentz-invariance

    I am well aware that spatial discreteness is in conflict with Lorentz-invariance. If there were a theory of QG that proposed Planck time as the smallest interval of physical time, would that be in conflict with Lorentz-invariance?
  5. Battlemage!

    I Does Planck Time Imply an Acceleration Limit?

    Mods, I wasn't sure whether to put this in quantum physics or relativity, but since the speed of light is the limiting factor I chose here. Move wherever you think is best. Okay so the speed of light is the asymptote for the speed that objects can accelerate to, and the Planck time is the...
  6. Adgorn

    Planck time at the speed of light

    I know that if an object moves at the speed of light, from its persepctive time will stop to a halt. However the smallest unit of time should be the plank time. So my question is, will the object (say a photon) experience throughout its life a single still "frame", or will it experience...
  7. B

    B 2 events in a planck time not violate conservation of energy

    This thread is about a topic that unexpectedly came up in my thread titled "Contradiction between Cosmos and what someone here told me?". I will subsequently call that thread "Contradiction" for brevity. I am not sure if this thread belongs on the Quantum Physics forum or the chemistry forum...
  8. skepticwulf

    B Object projected vertically upwards and Planck time

    When we throw an object vertically , its speed decreases due to gravity and comes to a halt at the very top, V=0 and starts falling down. What can we say about that "halt" moment? Is it defined in terms of seconds? Does it last as long as Planck time? being the smallest measurement of time that...
  9. bbbl67

    I Can interactions happen at less than the Planck Time?

    I was watching this PBS Spacetime video, and something they said bugged me. They said that some subatomic interactions are occurring at time scales less than the Planck Time. And thus, this would also mean that these things are happening at scales less than the Planck Length as well. My...
  10. B

    What was the role of Hawking Radiation in the early universe?

    Amount of Planck energy is 1.956 * 10^9 J. Was this total energy of universe at plank time at big bang cosmology model? It's clear this amount of energy is not enough for making our solar system, even it's not enough for making mass of me ( 60 kg ). Should we postulate energy increase in the...
  11. C

    Size of Universe: Planck Time to Inflation

    What do we know or speculate as to the size of the visible and entire universe between the Planck time and the beginning of explosive inflation?
  12. Isaac0427

    Understanding the Planck Scale

    Hi, So I am a little confused on the Planck scale. Correct me if I'm wrong (I hope this doesn't sound idiotic) but I believe that any field on a classical scale should be able to be quantized and work on a quantum scale/Planck scale, where the Planck length and the Planck time are the...
  13. S

    Absolute time, local time, planck time

    While Planck time is usually regarded as the shortest unit of time, isn't the shortest unit of time that can exist is the time it took to go from absolute time, the big bang, to everything after that i.e. local time? Did local time exist at the instant of the Big Bang?
  14. apeiron

    Why is Planck time scaled by c^5?

    Just curious. The Planck length is lpl = (hG/c3)1/2 = 10-33cm And it seems intuitive that it's c cube because space has three dimensions for the action. But the Planck time is tpl = (hG/c5)1/2 = 10-43s So is there some obvious physical reason why c is to the power of five here?
  15. M

    Is Planck Time and Length the Smallest Possible Units of Measurement?

    Hope someone can clear this up for me, is Planck time the shortest possible time in which a particle or quark or anything can perform some kind of action? Also is Planck length the shortest distance in which an object can actually move? Anything shorter than that and the object doesn't mean...
  16. S

    Planck Time? Why does it exist?

    I've recently heard of Planck Time.. I read that it is the minimum time interval that can EXIST. What exactly changes in time intervals that are less than Planck time? And if I am not mistaken by the meaning of Planck Time; What is the reason that there is such a limit? For Example, the...
  17. T

    The universe, planck time and the game of life

    Is the universe similar to Conways game of life? Let me elaborate. For us, a second is the unit of time and its a pretty short unit of time. But then at the atomic scale, a second is a pretty big unit of time. Everything we do is in the order of seconds or maybe milliseconds. But so much happens...
  18. S

    Planck Time Problem: Calculation & Explanation

    Homework Statement Hi Guys, Just started a Mechanical Engineering Course and in my Physics this came up, I'm really confused and don't know were to start. I was wondering if anyone could shed any light on the subject. Thanks guys. Three of the fundamental constants of physics are the...
  19. B

    Exploring the Theoretical Nature of Planck Time with Michio Kaku on Cspan BookTV

    I was watching indepth on cspan booktv with Michio Kaku and he says that the Planck time has not be proven. I thought it was a proven fact, but he says it is still theoretical and we have no evidence for it yet. Is this true?
  20. D

    Is planck time the same in all reference frames?

    Quick question: Is Planck time the same in all reference frames? Is it different at, say, half the speed of light than at a relatively stationary point? What about in a severe gravitational field, like a black hole?
  21. N

    Deck of Cards and Planck Time?

    Deck of Cards and Planck Time? This is truly unbelievable. I've checked my work multiple times, gotten it checked by others, and still the same answer remains. There are more ways to rearrange a single deck of cards than there have been Planck times since the Universe began. Number of...
  22. Z

    Finding Planck time in terms of [G], [h], and [c]

    Homework Statement Find a set of 3 exponents a, b, g such that the quantity [G]^a [h]^b [c]^g has dimensions of time. In other words: [T] = [G]^a [h]^b [c]^g (hint: you should get 3 algebraic equations in the 3 unknowns a, b, g which are not that hard to solve. Now determine the socalled...
  23. H

    Sampling at 1/n Planck Time: Synchronizing Samplers and Analyzing Data Values

    Can we synchronize n samplers so that the system is being sampled at 1/n Planck time? What could we tell about the data values between two adjacent samples?
  24. K

    Textbook talks about Planck time

    A section in my textbook talks about Planck time, but I still don't quite get what does it mean after I finished reading it. I am also wondering whcih laws of physics can be applied to the Planck time. Some info that might be helpful for answering this question: tp=√(Gh/c^5) where G is the...
  25. F

    Reconciling Non-locality and Planck Time: Exploring the Limits of Causality

    How does instantanious action at a distance reconcile itself with Planck Time and the assumption that nothing can happen in this minuscule timescale? Does the transition from cause to effect not have a Planck time after the cause and before the effect? Could one describe a unit of Planck Time...
  26. C

    What is Planck time, Planck length, Planck particle

    Can someone explain what are they: For egs. What is Planck time, PLanck length, Planck particle etc.
  27. V

    Can Planck Time Explain the Age of the Universe?

    O.k., so I'm reading this article by victor stenger called Fitting the Bible to the Data where he is criticizing this guy Schroeder's attempt to fit the bible creation story in with big bang cosmology. he chooses the time of quark confinement, or 10^-4 seconds to start. this is the part that...