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Questions tagged [time]

Time is defined operationally to be that which is measured by clocks. The SI unit of time is the second, which is defined to be

The SI unit of time is the second, which is defined to be

the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

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What is an instant of time?

If we say that an instant of time has no duration, why does a sum of instants add up to something that has a duration? I have a hard time understanding this. I think of one instant as being a 'moment' of time. Hence, the sum of many instants would…
james
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If we suddenly lost track of time, how would we know what time is now?

If we hypothetically lost all watches and all devices that keep track of time, how would we say what is the current time? Or we actually don't and time is just a convention?
matt_zarro
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Time, what is it?

If you ask any person about time, she/he will give you some answer. I suspect that it is extremely difficult, (if not impossible) to define time. Is there a definition of what it is in physics? Is it an "axiom" that has to be taken as it is,…
user6090
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How might clock synchronization work with RSA SecurID tokens?

My workplace uses these things to generate one-time passwords which only work within a short time period. I have always been curious about how the clock synchronisation between the authentication server and the token might work. I'm not sure…
wim
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What is a clock?

Relationalists love to define time operationally as what clocks measure, but this begs the question of what counts as a clock. Clearly, it's a measuring instrument and what it measures is supposedly time. We need to avoid circular definitions of…
Velazio
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If the entire universe is the same age, can one assume that any potential life elsewhere is at the same stage of development as us?

There was some discussion in another question regarding whether you can consider all parts of the universe to have existed for the same length of time, and the conclusion seemed to be that, because of relativity, it depends. I'd like to know, in a…
spongefile
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What is time? Does it flow linearly? If so, how are we sure?

Distances in our world (classically at least) can be defined by considering our world to be a model for the Euclidean normed three dimensional space. But how can we set the notion of time on a firm footing? What are the first principles…
Atom
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What is a good definition of 'time'?

I know this is a silly question, but I'm only asking this because I honestly can't seem to find a good definition of time that doesn't include another word that relies on the definition (or logical understanding rather) of time. For example, in many…
Arturo don Juan
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Does really time exist?

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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Does time actually exist or is there just a single stateful system being updated over time?

What I mean is, is there a past, future and present? or just a NOW which changes? I'm a computer programmer so the second alternative is from my programming experience. In this second alternative, I mean to ask, are we just in a stateful system like…
Phil
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What makes us move in time?

Time is considered to be a dimension, and we are moving at certain rate in one direction in time. What force makes us move in time? I mean it must be ether time moving or us moving in time so there has to be some force that 'pushes'/'pulls'? Was…
Matas Vaitkevicius
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How can we know the time frames for events in the early universe?

I just finished watching Into the Universe with Stephen Hawking (2010). Specifically the third episode titled 'The Story of Everything.' In the episode Hawking is explaining the mainstream theories of the events just after the Big Bang. What…
user21380
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If I could stop ALL motion would I stop time?

I've never really understood time. Time is not a force. It isn't energy or matter. Time doesn't MAKE anything do anything. Time doesn't make a clock tick (motion or batteries do). Time doesn't make the earth revolve around the sun (motion/gravity…
Stuart Sloan
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Is time really necessary?

In classical mechanics the coordinates of a particle are functions of time. That path is a solution of the equations of motion. In principle then it is just a parameter and can be eliminated giving a direct relation between the coordinates E.g. If…
Robbydcm
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Would time exist in a universe with only one elementary particle in it?

Imagine a universe infinite in all directions with only one elementary particle moving through it (impossible, but suppose). Can one define time in this universe?
Deschele Schilder
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