Geometric Cutoffs and the End of Time
A research paper suggests time itself will end in just 5 billion years. The ensuing catastrophe would be something we’ve never before witnessed.
Philosophy and physics overlap in many areas. They bleed into and feed one another with new ideas and predictions, changing our world views time and again throughout history. But there are perhaps fewer concepts in physics that tangle so much with philosophy as does the concept of time. Even defining it is difficult, though a rudimentary definition may say, “time is the fourth dimension which allows our three-dimensional world to experience change”.
Time is change. It’s the development from simple organisms swimming in a primitive ocean to the complex, ambling beings we are today. Our knowledge unfurls over the years, building on what’s come before it. To take away time or to imply that it has an end is to imply that there comes a point at which life can no longer survive. And that, according to work done by physicist Raphael Bousso and colleagues, may happen in the next 5 billion years.
The scientists worked off the foundation of eternal inflation. An extension of inflationary theory which helped resolve various problems in cosmology, eternal inflation says that the expansion of the universe never ends altogether but can end in small, local pockets. The background continues to expand but the pockets where inflation slowed or stopped became universes just like ours. In looking at the grander model of the universe, it is less as if inflationary theory is a triumphant part of the Big Bang theory and more as if our description of the Big Bang is an illusion — a mere hot and energetic marker in the more encompassing breadth of inflationary cosmology. But the Big Bang would not be a true beginning. If the universe is in a perpetual state of expansion, beginnings and ends don’t exist on a global scale.
And where eternal inflation can form one universe — ours — it has formed many more around us. This is the multiverse.
In this multiverse where there are an unending number of worlds, any event with a nonzero probability of happening will happen. And since there are infinite worlds, the event will happen infinite times. This is deeply troubling for calculating probabilities and knowing what physics we can expect to observe. Probabilities are relative. It’s all about how likely one outcome is to occur in comparison to another. But if both outcomes have an infinite chance of happening, it would make calculating any probability pointless. This is the “measure problem” of physics.
So emerged the geometric cutoff — a point after which time no longer exists. This means the number of events would be reduced to a finite amount and the relativity of probabilities again makes sense. The mathematical cutoffs take a once gargantuan and infinite universe and make it into a limited space where some events do happen more frequently than others.
The catastrophic end of time arrives just like any other moment, except that now there is no “after”. For a person witnessing the end it would be much like crossing the event horizon of a black hole. Certainly a significant event is happening, but it wouldn’t feel dramatic or climactic. In fact, the end of time would be experienced without the observer even realizing anything is taking place. Other physical systems of our world wouldn’t have been affected beforehand, thereby giving the impression that the universe has carried on as usual and it’s only when the moment itself arrives that our existence is affected.
Sudden death. We may wake up one morning and tend to the new spring flowers, or make mushroom stew to share with our children at dinner. The washing machine vibrates as the background noise of our home. Night comes and we call our parents or our lovers before we go to bed in the inner-city hotel room or at the country home. But we won’t be alive the next morning and we’ll neither have known it nor felt any distress about it happening. Except in this case there is still life after a person’s death. The earth continues to chirp, blow, churn, freeze, and fume even after one of us is gone. And like the end of time, this might be a frightening prospect but it’s not a problematic one. Time is a system similar to any other which could eventually break down. According to the calculations by Bousso and his team, a universe that’s 13.8 billion years old will experience its cutoff in 5 billion years.
While geometric cutoffs are now only a mathematical tool in an attempt to understand events in the multiverse, mathematical tools have become reality in the past. Quarks, for example, were used in calculations long before anyone ever believed they were real. And they are funny particles; never seen in isolation, trapped inside the caging proton. And yet while they once only existed in the realm of mathematics they are now considered fundamental particles.
To avoid the end of time involves admitting that our mathematical predictions use invalid techniques, or that the inflationary theory that’s so far been very successful is wrong. And there are other solutions to the measure problem. The end of time is not something that is necessarily correct but merely a scenario which arises logically from our theories of general relativity, inflation, mathematics, and experimental data — namely data which reveals that our universe continues to expand.
Either geometric cutoffs must be replaced, or they signal the eventual fate of the universe.
One of the most striking sentences in the paper says that, “if the end of time is a real possibility, then it cannot be prevented just by refusing to ask about it.” We do not know what the end of time would bring just as we do not know what death will bring. But in our best scientific understandings, life itself arose from a nonliving swath of ocean. It came from the right mixture of chemicals and temperatures, though the normal state of the environment is one without life just as the normal state of the universe might be one without time. Different, but not paradoxical.
