I will explain it as best as I understand it, allowing for of course that I am no scientist, just an enthusiast
Thermodynamics teaches that in any closed system the amount of heat in that system will eventually reach equilibrium. So if the universe existed for an infinite amount of time before now, then all areas in the universe would be equally warm. Obviously, we can tell this is not true, because we can observe differences in temperature.
It also teaches that no new energy can be created, the existing energy when used is only recycled into a less usable form of energy. Using the same infinite principle, all energy would have become benign and unusable an infinite amount of time ago. In order for the clock principle to work, it would still require a self sustaining energy source to supply the turning of the clock hand or reader
A third understanding is that of course the universe is expanding and particles are drifting further and further apart. if this has been ongoing for an infinite amount of time, then our particles would be space dust, drifting ever apart.
So you see the laws of thermodynamics would need to be debunked in order to establish an infinite universe theory.
The mention of something "outside" the universe was premised on a finite universe theory (a universe with a beginning)and the term I used was likely fuelled by a preconceived bias, but perhaps I can explain. People who have a theory on the origin of the universe can usually be categorized into one of two categories, a belief in one of the two following statements
a) something caused nothing to become something
b) nothing caused nothing to become something
Considering a) something that caused the universe to be would have to operate outside of the universe and by nature would not be bound by its laws, alternately if b) nothing caused the universe to come about, the principle of causality is negated.
One way or another the natural laws that bind this universe have been compromised
Whenever I indulge a conversation on science I usually like to offer a caveat that I am sorry for any inaccuracies in my rudimentary understanding. I welcome any correction.