Is Time a Scalar or a Vector in Physics?

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The discussion centers on the nature of time and speed in physics, particularly whether they are scalar or vector quantities. Participants explore the implications of negative signs in equations, noting that while speed and distance are scalar and do not have direction, negative values can be conceptually linked to reversing motion. The conversation highlights that negative speeds do not equate to actual backward movement, as they lack real-world comparability. Time is primarily treated as a scalar, but in contexts like relativity, it can behave like a vector. The significance of negative signs and their placement in equations raises questions about their impact on understanding physical processes.
louis arthur
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I was looking at how speed = distance/time. Then i started messing around with negative signs in the equation and it gave me strange things to think about. I can put a negative sign on the top or bottom of the fraction side and I have a negative speed. When I think about traveling at negative speeds across negative distance, that is acceptable as an object driving away from me with the transmission in reverse. But if the negative sign is on the time side of the fraction, I think about that object moving the same as the former object. This messes up my concept of the entropy in the motion of these objects since the latter would have exhaust rushing into the muffler. I looked at each variable equaling the other two, and the various ways a negative sign can change the real life concepts of what is actually happening. In the end I sat there dumb-founded at the significance of the negative sign being on particular sides of the fraction, how it relates to the actual physical processes and why I was taught that where the negative is in a fraction is insignificant. I am new to thinking about science and math and such. Is this a real thing that is considered by physicists and physics students?

louis arthur
 
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Don't sweat the negative signs in the equation that you are considering. Just as you imply, you can run the "video" of the situation backwards or forwards in many situations. Negative signs show up lots of times, and you just have to think some about what they mean. Like the concept of negative frequency in spectral plots...that took me a while to get my arms around.
 
louis arthur said:
When I think about traveling at negative speeds across negative distance, that is acceptable as an object driving away from me with the transmission in reverse.
I don't think that's right. Speed and Distance are both scalar quantities - they have no direction to them. So (unlike velocity), a negative speed does not mean going backwards - it's not really comparable to anything in the real world.
 
Libertine said:
I don't think that's right. Speed and Distance are both scalar quantities - they have no direction to them. So (unlike velocity), a negative speed does not mean going backwards - it's not really comparable to anything in the real world.

As you quite rightly said, distance and hence speed are scalar quanities. However, it is therefore impossible to have a negative speed. Negative times do not usually occur because we are usually trying to find out what happens after an event (t=0), a ball being hit, or a projectile being fired etc.
 
is time a scalar quantity?
 
Under normal cricustances, time is a scalar. However, under some circustances, such as when considering relativity, time can be considered a vector quantity. An example of this would be the 'light cone' http://en.wikipedia.org/wiki/Light_cone :smile:
 

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