Isn't this just an argument about definitions? It makes no sense to say that the universe has 0 size from a photon's reference frame and it also makes no sense to say the photon has a reference frame, but intuitively the experience of space "shrinking" with correlation to higher velocity for the viewer in some reference frame suggests that the as the reference approaches the speed of light, the length of space approaches zero, and while it makes no sense to speak of something with mass traveling at the speed of light, the intuition is that from that imaginary perspective space has no size.
> the experience of space "shrinking" with correlation to higher velocity
This is not a good description. Length contraction is not a real process of "space shrinking"; it's a matter of perspective, similar to the way objects can have different apparent sizes in ordinary geometry depending on which direction you look at them from. An object moving with a high velocity relative to you is "rotated" in spacetime relative to you such that it appears shorter; but the object itself is unaffected.
Notice that I said "high velocity relative to you"; this is another way of seeing why "space shrinking" is not a good description. Velocity is relative: "high velocity" relative to you is not the same as "high velocity" in an absolute sense (there is no such thing). So saying that "space shrinks at high velocity" doesn't make sense.
I understand that space "shrinking" is a perspective (which is why I originally placed it in double quotes) and that velocity is relative - my question was meant more as a thought experiment of taking the subjective experience of what things seem like as relative velocity increases and then extrapolate it to what they might seem like as relative velocity approaches the speed of light, i.e what would experience be like were it possible to ride on a photon. Since riding on a photon is not possible, perhaps this question is meaningless - it's just that since there is a pattern to how space is experienced with increasing relative velocities, the tendency is to extrapolate this to try and imagine how space/time would be experienced if it were possible.
That being said, I understand that a "universe of length zero" or "no time" is not relevant nor practical in the context of doing physics.
> what would experience be like were it possible to ride on a photon
But that's not what "space shrinking" represents. The object or person that is moving at close to the speed of light relative to you does not see their own space shrink. Their "space" appears to you to "shrink" (I put the words in scare-quotes because of all the issues I already brought up). So even if "space shrinking" is a reasonable interpretation of something, that something is not what you would even want to extrapolate to "the experience of riding on a photon" (which is meaningless anyway, as I said in my other post just now), because it doesn't describe the experience of the observer moving at high speed relative to you, it describes your own experience, and to yourself, you're at rest.
Isn't this just an argument about definitions? It makes no sense to say that the universe has 0 size from a photon's reference frame and it also makes no sense to say the photon has a reference frame, but intuitively the experience of space "shrinking" with correlation to higher velocity for the viewer in some reference frame suggests that the as the reference approaches the speed of light, the length of space approaches zero, and while it makes no sense to speak of something with mass traveling at the speed of light, the intuition is that from that imaginary perspective space has no size.