Telescopes can look back in time because light takes time to travel from one place to another. When we see distant objects, we are not seeing them how they are now, instead, we are seeing how they are when they emitted that light. For example, JWST spotted the death of a star about 2500 light-years (2500 * 9.5 trillion km) away. So, that death of a star happened not now but 2500 years ago.