One summer night when I was outdoors, I stared skyward in reflection and pictured myself in an all powerful vehicle that could sail indefinitely on and on. In my flight of imagination, I took off far above the clouds and into the expanse beyond. My mind transported me past distant planets, crossing the remote outskirts of our solar system where comets were swinging near their aphelions, and I voyaged far and still farther away from our own solar system, amidst stars and more stars, and then I moved even beyond the periphery of our own galaxy, away from its billions of stars, and zoomed still way over there, passing millions of galaxies on the way.
On and on I went and I never encountered a stopping sign that said, “Here endeth Space.” Tired and disappointed, I came back again to here below. I was impressed that with my mind I could travel such distances and return home so quickly. I couldn’t have indulged in that fantasy if the efforts of physicists and astronomers had not made me aware of grand stretches and galaxies. Science heightens our awareness of the world and it raises our consciousness to levels and realms that normal perception seldom uncovers.
It is difficult to think of a limit to spatial extension. Infinity is always baffling to the mind, and here is a perplexing endlessness that strikes us as reasonable, prompting philosophers and lay people alike to conclude that space goes on and on and on, limitless. But, if are to trust our current physics, this is only another of the illusions created by secretive Nature, for space does not extend indefinitely.
Indeed, if space extended without bounds and stars were distributed uniformly in the heavens, then it would follow – and this may be mathematically reasoned out – that the infinity of stars would light up the night sky as brightly as broad daylight. In earlier centuries, astronomers pondered this question, and concluded that there ought to be some distance beyond which there is no universe, no space. This is the famous Olber’s paradox.
Physical space extends only as far as material galaxies have gushed forth, and this surely isn’t ad infinitum. Since galaxies seem to be advancing relentlessly every which way, space too is stretching itself to an ever increasing dimensions. The cosmos, our astronomers tell us, is like one gigantic balloon that is being continuously blown to larger and larger sizes. We seem to be living in an expanding universe. What irony that on our own planet we are gradually running out of space! It is one thing to study the world in our vicinity and another to make statements about the world at large. But the scientific spirit, intent upon formulating a universal world-picture, is convinced that the laws of physics that obtain here in our neighborhood must be valid anywhere and everywhere: on the moon as in a distant galaxy millions of light years away. Physicists are persuaded that the grand features of the world will be the same for no matter who, from no matter where.
Sure, there will be local variations. Martians will see more than one moon, and creatures (if any) in a multiple star system will experience permanent daylight from the thousands of luminaries surrounding them. There are galaxies here and there, strewn all over, like ink spots on a white sheet, or mini-mounds on a plain meadow. Leaving aside such clustered clumps, the large-scale features of the universe are the same everywhere, even as a cup of water from any section of the ocean will not vary from place to place. The universe, we say, is homogeneous. And so is space.
And then consider the universe along any direction. We see some constellations along one direction, yet others along another. But again, the overall aspect of space is the same along all directions. It is like standing in the snow-white of Arctic wilderness or on scorching Saharan sand and looking every which way. It all looks the same north or south, east or west. The same is true from any spot in space. We look in every direction, and there is no significant difference in the panorama. The universe, we say, is isotropic, and so is space.
This view, or compelling assumption, by which the universe preserves common features from no matter where it is observed and along whatever direction, is what we call the cosmological principle. In a homogeneous and isotropic universe, only three things are possible: the universe remains static, it expands uniformly, or it contracts uniformly.
The world is a long episode of events mighty and meaningless. Space is the arena where things happen. As Bret Hare put it,
“Behind the curtain’s mystic fold / The glowing future lies unrolled.”
Take away space and there will be no place to put things in, hence no physical universe. We cannot picture a void of higher order where even space does not exist! But the conceptual power of the human mind is fantastic, and it can, through equations and ideas, bring forth in its field of vision utter nothingness consisting of but a single dimensionless point.
The goal of physics is to discover how the world is and would be, quite independently of the human mind. But here is a paradox, for it is like wanting to describe a scene without the use of words. A scene there well could be, but its description has to be in terms of a language. So whatever world there is, it is the conscious self which experiences it. Modifying Shakespeare one might say that all of space is a stage, and all matter and movement merely players and acting.
It would be hasty to conclude from this that there was no stage or show prior to the emergence of the human mind, or that there will be none if and when the mind melts away in some disastrous deluge. The grandest show of all must and will in all likelihood go on, even if there is no terrestrial audience to observe and applaud. But such a world of mute matter sans measuring mind would not be pictured or expressed, conceived, experienced or explained the way it is done by earthling-physicists. It would be like encyclopedias buried deep beneath the oceans.
This is a chilling thought, a world without a human mind, ticking on for eons, without a receptacle for color or a response to beauty, nor rejoicing at fragrance, sound, or touch. Yet, such a universe could well come to pass, if our current understanding of matter and energy and stellar life-spans has a grain of truth. But we find it hard to entertain the thought of a spectacle that will go on for ages in a hall where all seats are empty. There could be such a world, but in such a world there cannot be science, for science is the coherent interpretation of the world by a reflecting mind.