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In the real world, Is there an example of an infinite signal?

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closed as unclear what you're asking by Dilip Sarwate, MBaz, Matt L., hotpaw2, Peter K. Dec 11 '18 at 20:58

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    $\begingroup$ You mean a signal that extends from $-\infty$ to $\infty$ in time? Hmmm, think about it for a moment. $\endgroup$ – Matt L. Dec 11 '18 at 17:03
  • $\begingroup$ Imagine you could show a signal has existed from $t=-\infty$ (or from $t=0$ if you prefer)... How could you prove it will exist until $t=\infty$? $\endgroup$ – MBaz Dec 11 '18 at 17:11
  • $\begingroup$ @MattL. No, a signal that extends from 0 to $\infty$ . but, I don't no. :( $\endgroup$ – niloofar jamshidi Dec 11 '18 at 17:14
  • $\begingroup$ We can arbitrarily invent signals. For example, $s(t)=\sin(t)$ is infinitely long. Is that a real-world signal? I don't know – but if we say "the signal is the electric field strength of a plane electromagnetic wavefront over time, shot from earth into the vastness of space", that's a pretty real signal, and it's pretty infinite... $\endgroup$ – Marcus Müller Dec 11 '18 at 17:25
  • $\begingroup$ @MBaz In physics, the energy is always existed. is not possible boute the signal ? $\endgroup$ – niloofar jamshidi Dec 11 '18 at 17:25
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After the proposed heat death of the universe, no active life form will be available to measure the rest of any given signal. That's not a real world to anyone.

One could define a signal not as function of time but as function of location, and wrap around the location. An example is the present ambient temperature as function of distance traveled to the east from Pontianak, Indonesia, on the Equator. We don't know if the universe is infinitely large so measurements on a straight line would be a bit iffy.

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    $\begingroup$ :-) :-) :-) :-) $\endgroup$ – robert bristow-johnson Dec 11 '18 at 21:08
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    $\begingroup$ This would be a cyclo-infinite signal, if such a term exists. Good answer! $\endgroup$ – Dan Boschen Dec 12 '18 at 15:19

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