# Evidence of Time **URL:** \ **Category:** Factual Questions\ **Created:** [August 6, 2003, 11:39pm UTC](https://boards.straightdope.com/t/evidence-of-time/193458 "2003-08-06T23:39:53Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Meatros](https://avatars.discourse-cdn.com/v4/letter/m/b4bc9f/32.png) [@Meatros](https://boards.straightdope.com/u/Meatros)\ **Post date:** [August 6, 2003, 11:39pm UTC](https://boards.straightdope.com/t/evidence-of-time/193458/1 "2003-08-06T23:39:53Z")
I was talking with someone recently who had read a recent magazine (skeptic I think). He stated that time was metaphysical and that you couldn’t prove it existed. I didn’t have time to get into it further with him, but it made me wonder: Is that true? I mean we can measure time, so doesn’t that mean it’s not just a metaphysical concept? Then again, I also remember hearing that clocks will measure time differently (or something to that effect) depending on where you are. In any event, as you can probably tell-I’m not too clear on the concepts here, so I figured where better to ask then here :D. ---
**Author:** ![Zeldar](https://avatars.discourse-cdn.com/v4/letter/z/b77776/32.png) [@Zeldar](https://boards.straightdope.com/u/Zeldar)\ **Post date:** [August 6, 2003, 11:43pm UTC](https://boards.straightdope.com/t/evidence-of-time/193458/2 "2003-08-06T23:43:10Z")
Time is what clocks measure. It’s also the way we distinguish Past from Future. The notion of the flow of Time is primarily a function of memory. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 6, 2003, 11:49pm UTC](https://boards.straightdope.com/t/evidence-of-time/193458/3 "2003-08-06T23:49:11Z")
Time is what prevents things from all happening at once. You can’t really argue that it doesn’t exist. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 6, 2003, 11:51pm UTC](https://boards.straightdope.com/t/evidence-of-time/193458/4 "2003-08-06T23:51:11Z")
> [@](#): > > \*Originally posted by Meatros \* > Then again, I also remember hearing that clocks will measure time differently (or something to that effect) depending on where you are. This is somewhat true. The Newtonian concept of absolute time is not exactly correct. However, in Relativity, you have “time-like” and “space-like” things, so the the concept of time is not useless. Nor is the concept of a clock, something which measures time. Just because different observers measure time differently doesn’t mean that they’re not measuring _something_, even if the Universe doesn’t have a big watch that gives you The Time. ---
**Author:** ![jimpatro](https://avatars.discourse-cdn.com/v4/letter/j/b9e5f3/32.png) [@jimpatro](https://boards.straightdope.com/u/jimpatro)\ **Post date:** [August 7, 2003, 12:01am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/5 "2003-08-07T00:01:19Z")
Time is just our way of measuring the passing of events. There exists no physical entity called Time. Sorry Mangetout, your answer was very poetic but all kinds of things happen at once. All the time. Which gets me to the silly concept of time travel. Supposedly, forwards and backwards time travel is theoretically possible on paper. So is the Earth being hollow. So somehow it’s possible for things that no longer exist to somehow magically reappear again only backwards as we travel back? C’mon! ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 7, 2003, 12:05am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/6 "2003-08-07T00:05:59Z")
Sure, _multiple_ things happen together, it’s a big universe, you’d expect it, but not _everything_ happens all at once. Nobody is claiming that time is tangible, just that it exists as a phenomenon; that relativity causes it to slow down would seem to confirm that there is an ‘it’ to be slowed. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 7, 2003, 12:08am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/7 "2003-08-07T00:08:04Z")
In fact the concept ‘happen’ is meaningless without the passage of time. ---
**Author:** ![jimpatro](https://avatars.discourse-cdn.com/v4/letter/j/b9e5f3/32.png) [@jimpatro](https://boards.straightdope.com/u/jimpatro)\ **Post date:** [August 7, 2003, 12:14am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/8 "2003-08-07T00:14:00Z")
Not trying to send this to GD. But from what I recall, it has been demonstrated on spaceflight that clocks appear to slow down. Is this the best concrete example we have to support the THEORY of Relativity? The speeds involved nowhere approach C. Could there be some effect on the clocks that can be attributed to mechanical stress. I would really like to know if there is stronger evidence to support relativity. ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [August 7, 2003, 12:28am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/9 "2003-08-07T00:28:44Z")
> [@](#): > > \*Originally posted by jimpatro \* > Not trying to send this to GD. But from what I recall, it has been demonstrated on spaceflight that clocks appear to slow down. > Is this the best concrete example we have to support the THEORY of Relativity? The speeds involved nowhere approach C. Could there be some effect on the clocks that can be attributed to mechanical stress. > I would really like to know if there is stronger evidence to support relativity. Yes there is. A lot of it. Aside from the fact that relativity predicts the _amount_ that these clocks slow down, you also have (off the top of my head): Doppler shifting of relativistic jets. Extended lifetimes of muons entering the atmosphere at high speeds (close to c). Measured mass dilation of relativistic particles. The Michelson-Morley experiment. And that’s just confirmation of Special Relativity. For GR we also have: Perihelion advance of Mercury. Gravitational lensing, in a number of circumstances. The Shapiro time delay experiment. Time dilation/contraction on satellites in Earth’s orbit. GPS technology actually uses GR. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [August 7, 2003, 12:33am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/10 "2003-08-07T00:33:23Z")
**Jimpatro** , the clocks were different within experimenatl error otherwise you could draw conclusions about the correctness of relativity from them Well if your looking for larger margins of time dialtion, then muon (a type of meson) decay is what you want. Muons are formed in the Earth’s upper atmosphere by the collision of cosmic rays with air molecules and they have a half-life of about 1.5 microsecs. Due to the fact that they are travelling very close to the speed of light as they come down through the Earths atmospheretheir half-life is increased to about 30 microseconds, twenty times it’s original value because of time dialtion. ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [August 7, 2003, 12:34am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/11 "2003-08-07T00:34:28Z")
\*otherwise you **couldn’t** ---
**Author:** ![jimpatro](https://avatars.discourse-cdn.com/v4/letter/j/b9e5f3/32.png) [@jimpatro](https://boards.straightdope.com/u/jimpatro)\ **Post date:** [August 7, 2003, 1:03am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/12 "2003-08-07T01:03:43Z")
Okay, now in order for us to know that a Moun’s halflife has been increased due to it’s velocity we must have a control right? In other words a Muon at rest. Know what I mean. Do we have this? ---
**Author:** ![MC\_Master\_of\_Ceremonies](https://avatars.discourse-cdn.com/v4/letter/m/bb73d2/32.png) [@MC\_Master\_of\_Ceremonies](https://boards.straightdope.com/u/MC_Master_of_Ceremonies)\ **Post date:** [August 7, 2003, 1:20am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/13 "2003-08-07T01:20:37Z")
Yep, they can create low energy Muon beams, here’s a picture of the equipment: [http://lmu.web.psi.ch/lem/index.html](http://lmu.web.psi.ch/lem/index.html) ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [August 7, 2003, 1:26am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/14 "2003-08-07T01:26:26Z")
Time is the measurement of change. To deny the existence of time is to deny the existence of change, as all eternity would be contained in a single instance. But as soon as you open your mouth to deny the existence of time, you’re contradicting yourself. By the way, I’m curious to know your friend’s definition of the word “metaphysical.” He seems to mean “subjective,” which is absolutely not the same thing. ---
**Author:** ![Qwfwq](https://avatars.discourse-cdn.com/v4/letter/q/919ad9/32.png) [@Qwfwq](https://boards.straightdope.com/u/Qwfwq)\ **Post date:** [August 7, 2003, 6:30am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/15 "2003-08-07T06:30:49Z")
I remember a Joel Achenbach essay where he asked a physicist about time and the physicist told him he was asking the wrong person. There’s no inherent physical reason why time seems to move in one direction for humans–it’s a function of our particular neurobiology rather than a firm law of the universe. It’s debatable whether time is a relevant concept applied to photons, which by definition travel at the speed of light and thus define time for the slowpoke waves and particles around them, rather than being affected by it themselves ---
**Author:** ![EllisDee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ellisdee/32/4531_2.png) [@EllisDee](https://boards.straightdope.com/u/EllisDee)\ **Post date:** [August 7, 2003, 8:11am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/16 "2003-08-07T08:11:37Z")
There are 7 “arrows of time” found in physics. Off the top of my head: As time moves _forward_… …the universe expands …entropy increases … Dammit, I forget the rest. Lemme see if I can dig up that stupid book…\…crap, the SDMB is about to do maintenance, so I’ll repost in an hour. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [August 7, 2003, 10:06am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/17 "2003-08-07T10:06:57Z")
As others have noted, there is certainly no _absolute_ time. Objects moving relative to one another will “age” differently according to Einstein’s Special Relativity. As for "a direction of change (\*eg.\*entropy _etc_) then, as Boltzmann concluded, time can therefore run _both ways_ from a low-entropy configuration. It merely becomes a line connecting events: its “arrow” depends solely on the entropy at those events. I am currently reading Julian Barbour’s “The End of Time”, in which he really _does_ argue that there is **no such thing as time** , merely different “paths” between _simultaneously existing events_ (his “Nows”) in a configuration space (“Platonia”). I’ll start a GD thread when I feel up to it! ---
**Author:** ![RM\_Mentock](https://avatars.discourse-cdn.com/v4/letter/r/e274bd/32.png) [@RM\_Mentock](https://boards.straightdope.com/u/RM_Mentock)\ **Post date:** [August 7, 2003, 10:13am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/18 "2003-08-07T10:13:01Z")
> [@](#): > > \*Originally posted by jimpatro \* > \*\*Is this the best concrete example we have to support the THEORY of Relativity? The speeds involved nowhere approach C. Could there be some effect on the clocks that can be attributed to mechanical stress. > I would really like to know if there is stronger evidence to support relativity. \*\* The Dirac equation of quantum mechanics incorporated special relativity. ---
**Author:** ![EllisDee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ellisdee/32/4531_2.png) [@EllisDee](https://boards.straightdope.com/u/EllisDee)\ **Post date:** [August 7, 2003, 10:49am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/19 "2003-08-07T10:49:40Z")
Ah, found the book. > [@](#): > > _Quoted from Faster Than Light: Superluminal Loopholes in Physics, by Nick Herbert_ > The enigmatic status of the advanced solutions to Maxwell’s equations is part of a larger question in physics known as the “arrow of time” puzzle. The basic laws of physics, which include relativistic mechanics, Maxwell’s equations, and quantum theory, do not favor one direction of space over another–to go west is no more difficult than to go east as far as these equations are concerned. Similarly the basic laws of physics do not single out a particular direction in time: For a process to be pushed from the future to the past is just as permissible in these rules for the world as to be pushed from the past to the future. > … > For some unexplained reason, these time-symmetric laws have not resulted in a time-symmetric world, but have generated instead a world containing an “arrow of time” that makes one time “direction” different from the other. > > Actually there is not just one time arrow problem to be explained, at least six such mysterious arrows are embedded in natural phenomenon. These arrows are listed as: 1. Electromagnetic arrow (no advanced waves detected) 2. Psychological arrow (we perceive the passage of time) 3. Thermodynamic arrow (entropy increases) 4. Cosmological arrow (universe expands) 5. Quantum-mechanical arrow (wave function collapses) 6. Weak-interaction arrow (K-particle decays) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [August 7, 2003, 10:54am UTC](https://boards.straightdope.com/t/evidence-of-time/193458/20 "2003-08-07T10:54:19Z")
> [@](#): > > \*Originally posted by SentientMeat \* > \*\*I am currently reading Julian Barbour’s “The End of Time”, in which he really _does_ argue that there is **no such thing as time** , merely different “paths” between _simultaneously existing events_ (his “Nows”) in a configuration space (“Platonia”). \*\* I can see that this would be quite a good argument to the effect that ‘time isn’t really what you think it is’, but how can it be an argument that ‘time doesn’t exist’ (since it goes on to explain what (the author believes)time really is. A bit like saying that Shakespeare never existed; his plays were merely written by someone with the same name. [Next page](https://boards.straightdope.com/t/evidence-of-time/193458.md?page=2)