We see it frequently stated that in the subatomic/quantum world, there is no reason that the arrow of time points in only one direction, that either direction for particles is equally valid and workable. (If I am mis-stating this let me know.) But what is the model of the universe that is proper for a particle, or for that matter, anything with mass, regarding the particle itself. Is a particle to be seen as a long thin noodle that stretches from it's beginning to it's end, with a pointer as to where the current time you are observing and it is interacting, indicating the present according to your observation? And if this is the model, then would the particle's mass be the sum total of the entire noodle? Or is the proper model, a series of snapshots, perhaps trillions per second or more, each snapshot a complete picture of the universe and it's interaction with our particle (which way it's traveling through space, it's velocity, etc. This would be a huge snapshot since in essence that one particle interacts in at least a gravitational way with the rest of the universe.) What is the particle's real mass in this model? It's instantaneous mass of a single snapshot? A series of snapshots that make up one wavelength of whatever frequency is applicable to the wave function of the particel? Or is it only the mass in the present frame or a summation of all the snapshots combined? Or is the model for the particle something that only exists in the moment, that in what we call the present or past, that it no longer exists, like a traveling wave on a still pond, the wave only existing where it is at the moment, no hint of it behind it or ahead as it passes. In this model it would seem it has only the mass we observe. This seems to me to make some sense. But if this model is true, it seems to say there is no past or future to move to, that there is only the present for any particle, which I believe would hint that time travel is a fantasy. And finally are massive particles such as a neutron or proton, subject to different universal models of time and mass, than say a photon or maybe a neutrino? The reason I ask, is that it seems that to understand something like time travel in any serious way, or argue as to it's possibility or its possible complications (I went back in time and shot my grandfather), then one has to be working with the right model of what time is, especially when it comes to the relationship of time and mass, since after all that would be one of the more likely objectives of time travel, to be able to move through time as well as space.