Professional scientists define time via the assertion that “time is what clocks measure”. History, on the other hand, defines time via the concept “if two entities exist at the same time and place, they can interact”. What bothers me is that the two definitions are entirely contradictory; i.e., there exists no collection of clocks which will display exactly the same time for the relevant interactions of interest to humanity!
If you look at the “scientific” definition of time, it has already been shown that an official clock (the correct time by definition) will run at a different rate if it is raised or lowered in a gravitational field. If that is correct, how can a specific time for any interaction be quoted? Different people approaching the meeting via different paths can not possibly know the correct time of their meeting via the “scientific” definition!
Give me a good answer to that question and I will salute you!
Of course we know that time is not a constant but a relative dimension. It feels pretty consistent to us only because we move so darn slow. But the only “real” definition of time is distance divided by speed, with the speed of light being the only constant.
We should just “guess” about the definition of time? All I am asserting is that we need a well thought out definition of time. I have one if you are interested! I define time as a reference number associated with interactions. These “reference numbers” refer to specific fact which we believe to be true ; i.e., an event we have experienced.
I define “the past” to be that collection of events we have experienced. I define “the future” to be events we have not yet experienced. And, lastly, I define “the present” to a new event to be assigned to “the past”.
I further define the universe to be represented by a “four dimensions” coordinate system (x,y,z,t) which is capable of displaying the knowledge we have acquired. Note that this system essentially yields two different times to every event: one is the time assigned by our supposed understanding of the universe and a second being the time assigned by our becoming aware of the specific event.
If that is totally beyond your comprehension, don’t bother to answer this post.
Why not? It’s exactly what time is. When light has traveled 299,792,458 meters relative to a given observer, then the observer has experienced 1 second of time. It will vary from one observer relative to another depending on the observer’s own speed, so there is technically no universal experience of time.
Time is not an invariant quantity because two physicists (let’s call then Leonard and Sheldon) who leave home together and, due to some domestic argument, travel in to the university separately, will not be able to agree on what time has elapsed when they meet again over lunch. This is a relativistic affect caused by the bus Sheldon took being somewhat slower than Leonard’s car. Neither will they be able to agree on the distance back to the apartment as space is also not an invariant. However, as they can agree that they are both currently in the same place, there must be some invariant quantity. That quantity is called Spacetime. Being good physicists both can agree on how far they have travelled in spacetime, it is just a shame they could not agree on what brand of OJ to buy.
The difficulty is not scientific, but linguistic. Our language fails to give us words that have distinct enough meanings to talk about it unambiguously.
Space is defined as the relationship of objects at different positions. Time is the relationship of events at different , well, times. Sadly, we have two words for ‘space’ and ‘position’. But our language fails to deliver two different words for ‘time’ and ‘time’ in those separate contexts.
So, although we fully understand the difference, we have no vocabulary to unambiguously say the we understand it.
If it is necessary to schedule an event with such precision that different attendees might arrive at different times due to relativistic effects, then one would simply specify the frame of reference of the official clock used to set the time for the meeting to start. All attendees could then compare the clock’s frame of reference to their own and make the appropriate calculations. Just because different observers read different times on their clocks, doesn’t mean that they can’t calculate what others will observe.
If I say “in the past, before pterodactyls went extinct” – did we experience that, or was it not the past? If someone talks about what happened during the early days of the solar system, is it the past or isn’t it?
The OP’s “About Me” age says that he/she has a PhD in theoretical physics, so presumably he/she knows how professional scientists define time. (And given that level of education, why he he/she asking us?)
Tangentially related maybe but maybe someone can answer this for me as I know nothing of physics or relativity. Is the speed of light constant? I thought Einstein’s theory had something about the gravity say from the sun affecting photons or maybe it’s just that they bend?
I know that people bullshit on the Internet (and specifically here on the SDMB) all the time, but what’s the point of completing the About Me page if you’re just putting bullshit there?
It seems to me that despite what Einstein has said, it may well be possible to travel at speeds faster than light.
As I understand it, Einstein never said that the speed of light was an absolute and could not be exceeded. The truth would be closer to say that nothing can **accelerate **past the speed of light because as something accelerates toward the speed of light it’s mass becomes infinite.
By the way, I’m certainly not a PhD in anything - never mind Physics of any kind. And - if you can believe it - I am quoting a movie character named “**Prot” **who comes from the planet K-PAX.
If anyone is interested, you can check that out here:
And … yes … I do get all my knowledge from movies.
