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Asaf Pe'er

Physics for all

Does everything exist / happen at once?

The answer is obviously not. You could not be born before your parents; things do evolve - we see the changing seasons, etc. We use the concept of time to measure these changes, and discriminate between "past" and "future". We know what happened in the past, but we have no way of influencing it. On the other hand, we do not know what will be in the future, but what we do now can influence it (if you cook today, you will have food tomorrow...). What Einstein showed in his theory of special relativity, is that time is relative to the observer: two observers that are in motion with respect to each other and are looking at an event, will disagree on the time in which this event took place. But when a particular observer looks at two different events, the observer can easily tell which of the events was earlier and which was later.

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