Struggling to Understand Causality in Input-Output Relationship

[cybernoodles]

Hi All,

So I'm at the point where my brain is numb. I've been struggling for the past few hours trying to understand causality. Specifically, I have an input-output relationship y(t) = x(|t|). Determining if this is causal has been very difficult. Causal means that the output at any given time t is dependent on either the current input (present) or past input. So, if I plug in 5 to my output equation, I just get 5. How is that dependent on the past? I'm being told that this system is NOT causal, I.E. dependent on the past, which is really killing me.

 

[MisterX]

Consider the value of y when the parameter of y is negative. The value would be equal to the value of x with a positive parameter, which you may interpret as the output of the system depending on the future value of the system input.

 

[jim hardy]

x=y seems present tense.

x=∫y would include past?