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I was wandering whether time really "exists" or is it just a mathematical parameter used to describe how things change.

Suriya
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    Possible duplicate of Is there a proof of existence of time? or understanding time: Is time simply the rate change? – AccidentalFourierTransform Jan 09 '16 at 19:39
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    You have to define exist before you can ask this question. And you should think about why you put the word "just" in there; what is it about thew phrase that follows that requires you to deprecate it? – dmckee --- ex-moderator kitten Jan 09 '16 at 19:42
  • Do you have a clock? Does it exist and show time? If yes, then time exists. It's simply the number that the clock shows. – CuriousOne Jan 09 '16 at 19:42
  • A physical object is said to "exist" if we can touch it or see it or sense it by some other physical means. But what does it mean to say that a non-physical object "exists"? –  Jan 09 '16 at 19:46
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    I mean, does it exist in the same way space does or is it just as a mathematical tool as velocity or length is – Suriya Jan 09 '16 at 19:49
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    It exists in the same sense as space exists. Space can be measured with rods and time can be measured with clocks. Same difference. – CuriousOne Jan 09 '16 at 19:55
  • @CuriousOne and what is most important (IMHO), time can also be measured with rods! – AccidentalFourierTransform Jan 09 '16 at 19:56
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    @curiousOne But velocity or energy can also be measured, but that doesnt mean they exist, they are just quantities that arise from our description of the universe using mathematics. – Suriya Jan 09 '16 at 20:00
  • @AccidentalFourierTransform: Yes, that is obvious for the special case of constant motion. For the general case you need some sort of local clock. Maybe there is a smart way of measuring eigentime with rods and I just haven't thought about it enough. Constant comparison of ones own moving rod against the rod in the other system? Yes, I suppose that works... but isn't that a clock? – CuriousOne Jan 09 '16 at 20:00
  • @PabloXd: Energy is a quantity that has the ability to heat your house and that can kill you. The ontology of physics and science in general is that things that can potentially kill you "exist". If you don't agree with that ontology, then you need to go to the philosophy department, they may be thinking more to your liking. – CuriousOne Jan 09 '16 at 20:02
  • @CuriousOne e.g., you can define time by taking two mirrors facing each other, with a fixed separation. To measure a time interval you just count how many times$^1$ a photon bounces off the mirrors. ($^1$no pun intended...). You know, the typical thought experiments in SR when you use light for everything... – AccidentalFourierTransform Jan 09 '16 at 20:12
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    @curiousOne I think energy doesnt exist as something physical. Thermal energy is just velocity, which is the change from one place in space to another. That change is a process that exists, as matter exists, but energy? I think its just a useful quantity that humans use because it is conserved. Maybe I'm just saying stupid things but i like to reduce physics to the most fundamental things I can. – Suriya Jan 09 '16 at 20:12
  • @AccidentalFourierTransform: That's an electromagnetic clock using reflections of light in a high Q resonator... – CuriousOne Jan 09 '16 at 20:15
  • @PabloXd: Science is not philosophy. It doesn't care what "you think". In science you have to separate cause and effect and find definitions that describe them properly. Energy is defined as "the ability of a system to perform work". Unless you are willing to learn these definitions and how to apply them properly, you won't have much fun in physics. As you can see, the formal definition is completely independent of velocity and thermal energy. Learn it well because it has been chosen for good reasons which will become more obvious as you go along. – CuriousOne Jan 09 '16 at 20:20
  • @CuriousOne of course its a clock: it measures time. I was just saying that you can measure time by measuring length (which is almost tautological inasmuch $c$ is a defined constant). – AccidentalFourierTransform Jan 09 '16 at 20:21
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    @AccidentalFourierTransform By putting together that measurement you have built a light clock. That's kind of a tautology, of course, because you built a tool to measure time. – dmckee --- ex-moderator kitten Jan 09 '16 at 20:22
  • @AccidentalFourierTransform: You still needed a moving system for that (your light beam), which needed an energy source and a thermal sink. A clock is a device in thermodynamic disequilibrium. A rod is a device in thermodynamic equilibrium. They are not identical. I think it's the other way round: one can measure distance with clocks, but one can't measure time with rods, at least not if we subject ourselves to thermodynamics in addition to geometry. – CuriousOne Jan 09 '16 at 20:25
  • @Pablo Xd Time that is measured by clocks is surely something artificial,in this sense it doesn't exists.However there's a more deep definition of time as the direction in which events occur.https://en.wikipedia.org/wiki/Arrow_of_time (this link will explain it alot better than I can ever do) – Mr. Y Jan 09 '16 at 20:35
  • @CuriousOne I think the debate is taking us nowhere: we're just getting overparticular about unnecessary semantic issues (if a device measures time by measuring some length, is it a clock or is it a rod?). For the sake of friendship Ill back down. We could settle it by performing a Wick rotation, so that time becomes length (did ya hear, OP?: time is as real as space if it is imaginary) – AccidentalFourierTransform Jan 09 '16 at 20:51
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    @AccidentalFourierTransform: Thermodynamics is not a semantic issue. You are thinking about relativity in geometric terms, which is a very good level of abstraction for most issues. I am thinking about metrology in physics using fewer simplifications and I admit thermodynamics into my description of the measurement processes when I talk about time. It's not a matter of who is right or who is wrong, at all. We are both right and I never tried to say anything to the opposite. We are simply using two different levels of description, which is perfectly fair. Peace! – CuriousOne Jan 09 '16 at 20:55
  • @curiousOne Let me give you another definition of energy which is "funnier", a quantity that is conserved if all the particles of a system can be translated in time and nothing "changes". Do you really think the laws of physics are casualties or that are derived from deeper facts? – Suriya Jan 09 '16 at 20:57
  • @PabloXd: That's not a definition of energy but a description of Noether's theorem. Yes, you can look at it that way. Physical laws are shorthand descriptions of deeper properties of theories. Whether energy is actually conserved is, strictly speaking, unknown. There are plenty of people who are betting against energy conservation on the cosmological level. None of this has anything to do with your original question and false statement, of course. – CuriousOne Jan 09 '16 at 21:31
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    @curiousOne "None of this has anything to do with your original question and false statement, of course." the hell are you talking about? Does your discussion with AccidentalFourierTransform has anything to do with my question? Where did you study philosophy by the way? – Suriya Jan 10 '16 at 00:12
  • @PabloXd: I am a physicist, not a philosopher and philosophy is not welcome around here, if you haven't noticed, unless it tries to understand reality and wants to get help from the ultimate experts in reality. You don't sound like one of those and that's why your question has been closed. Have a nice life. – CuriousOne Jan 10 '16 at 00:15
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    @CuriousOne You could have been nicer, you dont need to beat a 15yo to show how much physics you know. What I meant with my question is "Does time exist as another dimension or its just a mathematical tool?" I dont see your point on energy, I think its just a product of our mathematical description of nature. I guess I'm more of a mathematician... (or philosopher) – Suriya Jan 10 '16 at 00:30
  • See my very first comment to you. Time in physics is that, which the clock shows. That is the correct answer. I wasn't "not nice" when I gave it to you. It's the same answer I will give to everyone who asks. It's the right answer if you want to actually understand what time "is" in physics. As you can see from my discussion with AccidentalFourierTransform, even colleagues are sometimes thrown off by it because it is both trivial and absolutely non-trivial: it forces you to think about the question "What are clocks?". – CuriousOne Jan 10 '16 at 00:36
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    @CurousOne time isnt "what clocks show". It can be another dimension, the change of a system or whatever but it isnt "what clocks show", its like saying length is what a ruler shows – Suriya Jan 10 '16 at 00:48
  • Length is what a ruler shows. A ruler is a tool which measures distances, so distance is what a ruler measures. A clock is a tool that measures time and time is what a clock measures. Nor are these definitions circular because we're able to look at two tools and compare how good a ruler (or clock) they are and then pick the better one to use. All of science is about operational definition because all of science is about being able to make reliable predictions. – dmckee --- ex-moderator kitten Jan 10 '16 at 03:05
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    @PabloXd I see that you're really genuinely puzzled by what time is at a really fundamental level.The only way you can really start to "dig" in this mistery is to study physics at university ,as that will give you the right tools to deal with your question.Don't be discouraged now ,and keep asking such questions . ;) – Mr. Y Jan 10 '16 at 08:44
  • @Mr.Y Yeah, I cant wait to get to university :D – Suriya Jan 10 '16 at 11:54

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