If the Great Questions of Philosophy left you with more questions than answers, that is probably a good thing.
Philosophy has a habit of doing that.
Once we start asking what reality is, whether we have free will, what consciousness is or whether life has a meaning, other questions quickly appear.
What is time? What happens when we die? Why is the universe so enormous? And how could anything exist in the first place?
Some of these questions belong partly to philosophy, others to physics, cosmology, neuroscience or religion. Many sit somewhere between them.
They are questions for which humanity has discovered some remarkable answers — but also questions where enormous mysteries remain.
Here are ten more great questions to explore.
1. What Is Time?
Time seems completely familiar.
Yesterday has gone. We are experiencing the present. Tomorrow has not happened yet.
But what exactly is moving?
We normally imagine time as something flowing steadily from the past through the present towards the future. Yet modern physics has made that picture much more complicated.
Einstein showed that time does not pass at exactly the same rate for everyone. Speed and gravity affect it. Two people can experience different amounts of time between the same events.
There may not even be a single universal “now” shared by the entire universe.
Then there is another mystery.
Why can we remember the past but not the future? Why does time seem to have a direction when many fundamental laws of physics work equally well forwards or backwards?
Perhaps time really flows.
Perhaps past, present and future all exist in some sense.
Or perhaps our experience of time tells us as much about consciousness as it does about the universe.
[Explore: What Is Time? →]
1b. What Is the Present? Does “Now” Really Exist?
2. What Happens When We Die?
We know what happens to the body after death.
The more difficult question is what happens to us.
If consciousness is entirely produced by the brain, then when the brain permanently stops functioning, presumably conscious experience ends with it.
But human beings have questioned this conclusion for thousands of years.
Could consciousness somehow continue?
Is there such a thing as a soul?
What should we make of near-death experiences?
And what would it actually mean for you to survive your physical death?
This last question is particularly difficult.
If something survives but has none of your memories, personality or experiences, in what sense would it still be you?
Death therefore leads directly back to some of philosophy’s oldest mysteries: consciousness, personal identity and the relationship between mind and body.
[Explore: What Happens When We Die? →]
3. Is There an Afterlife – and What Might Paradise Be Like?
The possibility of an afterlife appears in religions and cultures throughout human history.
But the possibilities are remarkably varied.
Heaven. Resurrection. Reincarnation. Rebirth. Union with God. Spiritual realms. Liberation from the cycle of existence.
Different traditions have imagined what lies beyond death in very different ways.
And this creates some fascinating philosophical problems.
Would we have bodies?
Would we remain the same age?
Would we remember our earthly lives?
Would we recognise the people we loved?
Could we still make choices?
And what would it actually be like to exist forever?
An eternal paradise sounds appealing — but eternity is a very long time.
Could an existence without danger, loss or death eventually lose some of the qualities that make experiences meaningful?
Perhaps the idea of paradise tells us something not only about what we hope might happen after death, but about what human beings believe makes life worth living now.
[Explore: Is There an Afterlife? →]
4. Why Is the Universe So Big?
Look into the night sky and most of what you see belongs to our own galaxy.
Yet the Milky Way itself contains hundreds of billions of stars.
And beyond it are vast numbers of other galaxies.
The scale is almost impossible to imagine.
This raises a wonderfully simple question:
Why does the universe need to be so big?
If conscious life is important, why is almost the entire observable universe apparently empty and inaccessible to us?
One possibility is that the question has things backwards.
Perhaps the universe does not need to be this large for us. Instead, we exist because a universe capable of eventually producing stars, planets, chemistry and life naturally becomes enormous.
Or perhaps life exists elsewhere too.
The question also challenges one of our most persistent assumptions: that the universe should somehow be proportioned to human existence.
Perhaps its vastness is mysterious only because we instinctively place ourselves near the centre of the story.
[Explore: Why Is the Universe So Big? →]
5. How Did the Universe Begin – and Could Something Come From Nothing?
The universe is expanding.
If we run that expansion backwards, the observable universe was once in an extraordinarily hot, dense state.
This is the foundation of the Big Bang theory.
But it immediately produces another question.
What came before it?
And if the universe had a beginning, where did everything come from?
It is tempting to say that the Big Bang describes something appearing from nothing.
But that is not really what the theory says.
Physics can describe the universe extremely early in its history, but our current theories eventually reach conditions where they are no longer sufficient.
Some cosmological models propose earlier phases, quantum origins or larger structures from which our observable universe emerged.
But even these possibilities lead to a deeper philosophical question.
Why does anything exist at all?
Why are there particles, fields, laws of nature or quantum possibilities rather than absolutely nothing?
And what would nothing actually mean?
No matter how far backwards we push our explanations, we seem eventually to reach one of the strangest questions humans can ask:
Why is there something rather than nothing?
[Explore: How Did the Universe Begin? →]
6. Are We Alone in the Universe?
If the universe contains an enormous number of stars and planets, it seems reasonable to wonder whether life has appeared elsewhere.
Perhaps even intelligent life.
Yet so far we have no confirmed evidence of an extraterrestrial civilisation.
This creates a famous puzzle known as the Fermi paradox.
If technologically advanced civilisations are reasonably common, why haven’t we encountered any?
Perhaps life itself is extraordinarily rare.
Perhaps simple life is common but intelligence is unusual.
Perhaps technological civilisations tend to destroy themselves.
Perhaps they are too far apart.
Perhaps we are looking for the wrong things.
Or perhaps humanity happens to be among the first technological civilisations to appear.
Discovering even simple extraterrestrial life would be one of the most important discoveries in human history.
Discovering another intelligent civilisation would be something greater still.
For the first time, humanity would know that intelligence, culture and curiosity had arisen independently somewhere else in the universe.
We would no longer be the only known part of the cosmos asking questions about itself.
[Explore: Are We Alone in the Universe? →]
7. What Makes You the Same Person Throughout Your Life?
Look at a photograph of yourself as a young child.
You probably say:
“That’s me.”
But what exactly has remained the same?
Your body has changed enormously.
Your appearance has changed.
Your beliefs, knowledge, ambitions and personality may have changed.
You have forgotten countless experiences the child in the photograph once had.
So what connects that child with the person looking at the photograph today?
Perhaps continuity comes from the body.
Perhaps from the brain.
Perhaps from memory.
Perhaps from consciousness.
Or perhaps the self is not a permanent thing at all, but an evolving story connecting different stages of a life.
This becomes even stranger in thought experiments.
If every part of something is gradually replaced, is it still the same thing?
If your memories could somehow be copied into another body, which person would be you?
Personal identity seems obvious until we try to explain it.
[Explore: What Makes You the Same Person? →]
8. Do Animals Experience the World Like Us?
A dog enters a room and immediately notices smells that we cannot detect.
A bat navigates using echoes.
Some insects perceive ultraviolet light.
Migratory animals can sense aspects of Earth’s magnetic field.
An octopus has a nervous system organised very differently from ours.
These creatures inhabit the same physical world that we do.
But do they inhabit the same experienced world?
Probably not.
This raises an intriguing possibility.
The reality each species experiences may be only a small selection from a much richer physical world.
Humans naturally assume that the world we perceive is simply what reality looks like.
But perhaps there is no single way that reality “looks”.
There may instead be countless windows onto it, shaped by different senses, nervous systems and forms of consciousness.
And then comes the harder question.
What is it actually like to be another animal?
Perhaps some aspects of another creature’s experience are fundamentally inaccessible to the human mind.
[Explore: Do Animals Experience the World Like Us? →]
9. Could a Machine Ever Become Conscious?
Computers can already perform tasks that once seemed to require uniquely human intelligence.
They can recognise images, use language, solve problems and generate new material.
But intelligence and consciousness are not necessarily the same thing.
A machine could behave intelligently without experiencing anything.
So how would we know if that ever changed?
Imagine an artificial intelligence telling you:
“Please don’t switch me off. I’m frightened.”
Would those words prove that it was frightened?
Perhaps it would simply be generating the response its programming made most appropriate.
But then another uncomfortable question appears.
How do you know that another human being really experiences fear?
You cannot directly enter someone else’s consciousness. You infer their experience from their behaviour, biology and similarity to yourself.
If machines eventually became sufficiently sophisticated, deciding whether they were conscious might become more than an intellectual puzzle.
It could become a moral problem.
If a machine could genuinely experience pleasure, fear or suffering, how should we treat it?
[Explore: Could a Machine Ever Become Conscious? →]
10. Are There Limits to What Humans Can Understand?
Human intelligence is extraordinary.
We have discovered atoms, decoded DNA, measured the age of the universe and developed mathematical theories describing phenomena far beyond ordinary experience.
But human brains did not evolve specifically to understand the deepest structure of reality.
They evolved because they helped our ancestors survive and reproduce.
This raises a humbling possibility.
Perhaps there are aspects of reality that the human mind simply cannot understand.
A dog cannot understand calculus.
A chimpanzee cannot understand quantum field theory.
No amount of patient explanation would change that.
The limitation lies in the structure of the mind doing the understanding.
Could humans have similar limitations without being able to recognise them?
Perhaps some of the problems that have puzzled philosophers for centuries — consciousness, infinity, time, existence itself — are difficult because we have not yet discovered the answers.
But perhaps some are difficult because the human mind is not capable of fully grasping them.
Future science, mathematics and artificial intelligence may extend our understanding enormously.
But there is no guarantee that reality has to be completely comprehensible to the kind of brain evolution happened to produce on Earth.
That leaves us with a remarkable possibility:
There may be truths about reality that exist, but that no human being could ever understand.
[Explore: Are There Limits to What Humans Can Understand? →]
The Questions Keep Going
Twenty great questions might seem like enough.
But every answer seems to produce another question.
What is nothing?
Is space infinite?
Could there be other universes?
Why do the laws of physics exist?
Is mathematics discovered or invented?
Could reality be a simulation?
What is the self?
What is love?
What is beauty?
Why do humans create art?
This is not a failure to find answers.
It is what happens when we begin looking closely at the world.
Science has answered questions that once seemed completely mysterious. Philosophy has helped us recognise hidden assumptions in the way we think. Religion has explored questions of purpose, existence and transcendence for thousands of years. Art and literature have approached human experience in ways that cannot always be reduced to arguments or equations.
And there is no reason to keep these worlds separate.
A question about time can lead from philosophy to Einstein. A question about death can lead from neuroscience to religion. A question about animals can lead from evolution to consciousness and ethics. A question about the beginning of the universe eventually becomes a question about why anything exists at all.
That is where exploring ideas becomes particularly interesting.
You do not have to accept somebody else’s answer simply because they are a famous philosopher, scientist or religious thinker. Learn what they discovered or believed. Understand their arguments. Look at the evidence. Consider the objections.
Then ask what you think.
Your answer may change as you learn more. In fact, being willing to change your mind is part of the journey.
There will always be another question.
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