No, the fact that we can see galaxies that are 12 billion light years away does not imply that the universe has already ended. The statement that the universe will end in 5 billion years likely refers to certain predictions or models regarding the future evolution of the universe, such as the eventual expansion and cooling of the universe or the potential fate of our own solar system. These predictions are based on current scientific understanding and are subject to ongoing research and refinement.
When we observe distant galaxies that are billions of light years away, we are effectively looking back in time. Light from those galaxies has traveled for billions of years to reach us, allowing us to observe them as they were in the past. The vastness of the observable universe means that we can see objects at different distances and corresponding earlier times in the history of the universe.
The current age of the universe is estimated to be around 13.8 billion years, so the light we receive from objects that are 12 billion light years away originates from a time when the universe was relatively young. It does not imply that the universe has already ended. The universe continues to evolve and change, and our ability to observe distant objects does not indicate their current state or the current state of the universe as a whole.
It's important to note that predictions about the future fate of the universe are based on various cosmological models and theories, which are subject to ongoing study and refinement. While scientists can make estimations and hypotheses about the long-term evolution of the universe, our understanding is still evolving, and future observations and discoveries may provide new insights and revise our current predictions.