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Comment by tomelders | Hacker News Reader

Time exists. It's the observed difference between two states.

Also, i am not a physicist.

I would argue that the concept of time is what is used to explain the transition between two states, not the difference between them. Time is not required for either state to exist by itself, but because the speed of light is finite it must take a finite amount of time to change one configuration of matter (state) into another one.

"Time" is just another word for "change".

The difficulty is in defining "change" and "transition" without using the concept of time. The circularity is difficult to avoid. This is the classic paper that started it all: https://en.wikipedia.org/wiki/The_Unreality_of_Time

Time is not necessary for change to occur, I would argue.

For example, how long does it take for a thought to disappear? I would argue it disappears in no time, or at least that it can do so. There isn't any transition period where only half a thought exists (what's the half of the thought "apple")?

If we're talking about physical reality/matter, however, it must take time, because of the limits of the speed of light.

Or that there really is only one unchanging state, and what you perceive to be the passage of time is really just a very particular configuration of your 'memory' through which you 'remember' a different state, and that hasn't really changed at all.

Is there not just one ever present now in which all thing change?

Theory of relativity would say that there are many 'nows', which one you're in depends on which frame of reference you're in :)

To a photon traveling at c, the birth, growth, and death of the universe happen simultaneously; so to a photon, there is no now. From its perspective, it dies just as quickly as it comes into existence.

> Is there not just one ever present now in which all thing change?

Sure there may be; but going by the hypothetical possibility I raised, there really isn't a now. The passage of time could be an illusion due to your memory being in a particular unchanging state that has existed 'forever'. Who's to say the 'now' that has just passed wasn't just you remembering it?

Exactly; it's the measurement of change. As long as things are changing, time exists. (The fact that this discussion is taking place proves it's existence!)

> As long as things are changing, time exists.

Except at the speed of light.

Which by definition is impossible to reach.

Photons reach it all the time. Therefore, time does not exist for photons.

How do you know it is taking place. Maybe it's a "solid" recording of events. You could only perceive time passing.

The issue with your definition can be shown when thinking about the absolute zero point (that is, 0°K): as per definition in this state, particles lack any kind of energy. Common tongue would say that it is "frozen". Now if this state lasts, let's say, indefinitely, time would be non-existent. As there is absolutely no change in the state of the particle.

PS: Although one could now argue that the act of observation changes its state.

Can that state exist?

Currently no.

As the universe approaches heat death, quantum mechanics dictates that particles jump between states randomly, such that passage of time cannot be measured meaningfully.

Not just two states but causality. Something causes something else to happen. Although Sean Carroll says causality is an illusion, everything is "pre-defined". This just happen to flow one direction at a macro scale.

>Time exists. It's the observed difference between two states.

For something to be said to exist, must it not be immediately observable in the present?

Since state is perpetually changing, isn't "the observed difference between two states" always an observation of the past and never the present?

Perhaps it is more precise to say that change exists rather than time because "the observed difference between two states" can never include the present state.

> For something to be said to exist, must it not be immediately observable in the present?

I don't know...if you define it as such, then yes. But does something need to be immediately observable in a frozen state in order to exist?

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