I wrote:
"As energy can`t be destroyed it had to be reflected by a hard short or
open." Keith replied:
"Or just stopped and stored."

Wave energy is energy in motion. No motion, no waves.

Keith also wrote:
"All of this is easily visualized by observing the amplitude of the P(t)
function at various points along the line."

Power as a function of time has the same amplitude in the forward wave
everywhere along the line. Same is true of the reflected wave.
Interference as demonstrated by standing waves has no effect on this.

Keith wrote:
"I would strongly suggest that no energy crosses these points in the
line where the voltage and current are always zero since p(t) is always
zero."

See my comment above on power as a function of time. Keith erred in
saying "points in the line where the voltage and current are always
zero", as where SWR volts are zero, amps are max, and vice versa.

I wrote:
"If energy were turned around before it reached the end of the line,
nulls more distant from the source than the turnaround point would not
exist."

Keith wrote:
"Not so,---."

There is no argument that can make wave interference where there are no
waves. In a lossless line, pre-existing waves could circulate forever.
But, our discussion relates to effects on actual lines.

Keith wrote:
"Try visualizing how a step function charges the line."

Totally irrelevant. SWR nulls are the result of phase opposition at
specific points produced by alternating waves. A step function changes
only when it starts or stops. Only during the changes does Zo apply
unless a line is terminated in its Zo. In this case there`s no reflected
wave to make a null. As Reg once said, "If your line were infinite in
length, you could measure Zo with your ohmmeter.

Best regards, Richard Harrison, KB5WZI