Lakshya said:I am still not getting how we can show it on a graph like time-like separation and space-like seperation.
To show it on a graph, just draw the past and future light cones of one of the two events, if the second event lies inside the first event's past or future light cone there's a timelike separation, if it's outside of the light cones there's a spacelike separation (and if it's right on the edge of a light cone there's a lightlike separation). A closed timelike curve is something unusual that only arises in weird situations in general relativity, if you're just learning about special relativity you don't have to worry about it. It basically indicates a spacetime that allows time travel into the past--a particle traveling on a closed timelike curve would have a worldline that forms a loop, so the particle goes back in time and becomes its own younger self. And I haven't seen the word "void" used as a technical term in physics, in ordinary speech it means basically the same thing as "empty space"--what was the context you saw this word used in?Lakshya said:I am still not getting how we can show it on a graph like time-like separation and space-like seperation. What about void and closed time-like curves?
Where did you read this? Can you give a link? A tachyon is a hypothesized particle that moves faster than light, so it could connect events that lie outside one another's light cones, but it wouldn't be in "another universe", it would just be a faster-than-light particle in our universe. Also, there is no evidence that tachyons exist, and I think most versions of string theory (along with other models of particle physics) don't predict that they should.Lakshya said:I have read on the net that there's another universe across light barrier which is a complete converse of our universe. In our universe the maximum speed attainable is that of light but in that universe the minimum speed attainable is of light. The tachyon is a particle of that universe and we will surely find many other particles of that universe with the help of string theory.
Are you familiar with the basic idea of general relativity, namely that spacetime is curved by mass/energy, and particles follow "geodesics" in curved spacetime? If not you can read http://io.uwinnipeg.ca/~vincent/4500.6-001/Cosmology/general_relativity.htm or this or the articles in the "fundamentals" section of this page. A closed timelike curve could only exist in a spacetime that was curved in a very unusual way that would allow geodesics to form closed loops...it's uncertain whether such a spacetime is actually possible.Lakshya said:Also I didn't understand closed-time like curves that how can a worldline be bent?
I still don't really understand the context--what parts of the universe are being "separated" here? Can you give a link to the page if it's online, or else the name of the book/article if it's not? It's possible you're referring to something like the giant void described in http://www.time.com/time/health/article/0,8599,1656529,00.html, if so "void" is just a non-technical term for a region of space that's relatively empty of matter, at least compared with the rest of the universe.Lakshya said:I am using void in the context umm... let me quote "The universe is separated by a void". In this line what does void means? And also I have read this term in many discussions.
Time-like curves are paths or trajectories in space-time that represent the motion of an object. These curves are called "time-like" because they follow the direction of time, meaning that any event along the curve can be causally connected to events before and after it.
Light cones are imaginary geometric shapes that represent the possible paths of light in space-time. They are significant because they illustrate the limitations of causality in the universe – events outside the light cone cannot influence each other, and events inside the light cone can affect each other.
Time-like curves and light cones are closely related because the shape and position of a light cone can determine the path of a time-like curve. Time-like curves can only exist within the boundaries of the light cone, as they follow the direction of time within the constraints set by the speed of light.
A void in space-time is an area or region where there is a complete absence of matter and energy. In other words, it is a space where nothing exists. The concept of a void is often used in theoretical physics to explain certain phenomena, such as the expansion of the universe.
These concepts help us understand the nature of space and time by illustrating the limitations and constraints that exist within our universe. Time-like curves and light cones show us how causality works, while voids demonstrate the vastness and emptiness of space. Together, they provide a framework for understanding the complex relationships between space, time, and matter.