The scientists however accept the existence of matter. Therefore it should not be a problem to accept that the nature of matter is that it deteriorates. Whatever we see around us will be finished at one point: our house, our clothes, the trees growing outside, etc. The body is made of matter and therefore it cannot work forever either.
Just like in your childhood you had a small body. That is no longer existing. That means you have changed your body. Similarly, you'll have to change this body. When this body will not work anymore... Because it is material. Every material things deteriorate and it becomes useless at certain length of time. Any machine, any clock... Therefore it has been taken as dress: vāsāṁsi jīrṇāni yathā vihāya [Bg. 2.22].
However, according to the Vedas, the living entity is eternal. Although our childhood body is gone, we have not died. Therefore the logical conclusion is that our consciousness must continue even after death. How, where, in what type of body that we cannot perceive through our imperfect senses directly. That is impossible. What is possible though is to understand its existence by the process of hearing from the perfect source.
Anything which is beyond the scope of experience by our imperfect senses can be realized fully by the sound representation. A person transmitting sound from a far distant place can be factually experienced. If this is materially possible, why not spiritually?
SB 1972 1.5.38 purport
If we talk to a friend on a walky-talky, we cannot see him, nor can we hear him. What we hear from the walky-talky is actually not his voice directly, but it is a sound representation of his voice, which is produced by the speaker of the walky-talky. It is not true that by hearing the sound representation, we are bereft of experiencing what he says. In fact, in terms of receiving the information, which is being transmitted, there’s no difference between hearing his voice and hearing the sound representation of his voice. It is not difficult to conclude then that if a person who we are hearing from has a factual experience of a phenomenon and if he describes it to us as it is, our experience is direct. In fact, it can be more direct than actually experiencing the phenomenon by our eyes. Coming back to the example of the sun which to our eyes appears as a yellow disc, if we hear from an astronaut on a walky-talky who is actually seeing the sun planet right now from all angles in his spaceship, we are experiencing the sun more perfectly through hearing than through seeing the sun directly with our eyes.
Similarly, we can still have the proof of the soul’s existence in the next body not through seeing it in front of us, but through hearing from the Vedic scripture (a recorded sound). How do we know that the Vedas are correct? Same process –through hearing (studying them). Just like the modern man takes the word of a scientist for granted on so many things without unnecessarily going through the research himself, throughout the history, all classes of transcendentalists are accepting the authority of the Vedic literature. The authority might be different in the two cases, but the process is the same. We get to know about things which are beyond our perception by hearing from someone who has that perception. Either we believe the Vedas or the scientists, because we’re in ignorance we have to believe someone in order to learn new things. The difference is that in the case of modern science the conclusions change, whereas the Vedic conclusion, which is not tinged by material influence of mistake, illusion, imperfect senses and tendency to cheat remains. Vedic statements are a fact in the past, present and future and many of them have been actually confirmed by modern science as well whereas the so-called scientific facts such as man came from a monkey or life comes from matter were conceived at one point and will similarly vanish at one point because they’re manufactured in the factory of an imperfect scientist’s mind.
Karandhara. The basis of what they call "scientific integrity" is that they talk only about what they can directly experience.
Śrīla Prabhupāda. You may talk about your experience, and I may talk about my experience. But why should I accept your experience? You may be a fool, so why should I also become a fool? You may be a frog, but suppose I am a whale. Why should I take your well as all in all? You have your method of acquiring scientific knowledge, and I have mine.
Life Comes From Life: Life on Other Planets
The modern man has a tendency to reject dogmatic thinking and form his own conclusions based on various sources of information. Why not therefore give receptive hearing to a tradition, which has been here for thousands of years and still remains scientifically accurate? Make an experiment. What is the objection? As the Vedic scriptures are the only source of knowledge known to man, which actually explain the nature of the soul in such a detail, we actually have no other choice than at least study what they say.
As far as the soul's existence is concerned, no one can establish his existence experimentally beyond the proof of śruti or Vedic wisdom. We have to accept this truth, because there is no other source of understanding the existence of the soul, although it is a fact by perception. There are many things we have to accept solely on grounds of superior authority. No one can deny the existence of his father, based upon the authority of his mother. There is no other source of understanding the identity of the father except by the authority of the mother. Similarly, there is no other source of understanding the soul except by studying the Vedas.
One might ask however, at this point, what distinguishes such process of hearing of the Vedic literature from blind faith. Although the Vedas might give a very logical and minute description of the soul’s existence after the body’s demise, we’re still in doubts –it might be true, it might not be true. Because we cannot perceive the soul’s presence, are we doomed to be in such doubt forever?
This is of course an intelligent question. We should mention however, that besides the information about the soul’s nature, the Vedas also give a process by which one can actually have a direct experience of the soul’s eternality. If one follows the process, he can have a direct experience of what he has learned from the Vedic scriptures before. So it is not a blind faith. It can be verified. There’s a hypothesis and there’s an experiment. Simply we have to be willing to undertake it in the following way.
In the conditioned state, our pure perception of the self is covered. Daily we identify with the senses, with the mind, with the intelligence and with our false ego and thus identified we look for happiness. Although the soul is eternal and thus cannot be satisfied by temporary pleasures, we are again and again trying to enjoy materially and hope that one day we will succeed. This is actually the blind faith. We have subjected our perception to be controlled by such a lust and it is for this reason we have difficulty to perceive our eternality, although it is a fact by perception.
The aim of yoga is to come out of such blind faith and become free from the different coverings on the soul and act with the pure self in relation to the source of all pleasure, Supreme Absolute Whole –Krsna.
Prabhupāda: Actually soul is above intelligence. Above intelligence. Our gross senses, that is our present perception, direct. And beyond these gross senses, there is the mind. And beyond the mind, there is intelligence. And beyond intelligence, there is soul. So come to that platform requires that meditation process to make the sense activities calm and quiet, mind settle, and then come to the intelligence platform, then come to the spiritual platform.
Room Conversation with Dr. John Mize -- June 23, 1975, Los Angeles
indriyāṇi parāṇy āhur
manasas tu parā buddhir
yo buddheḥ paratas tu saḥ
The working senses are superior to dull matter; mind is higher than the senses; intelligence is still higher than the mind; and he [the soul] is even higher than the intelligence.
The senses are different outlets for the activities of lust. Lust is reserved within the body, but it is given vent through the senses. Therefore, the senses are superior to the body as a whole. These outlets are not in use when there is superior consciousness, or Kṛṣṇa consciousness. In Kṛṣṇa consciousness the soul makes direct connection with the Supreme Personality of Godhead; therefore the bodily functions, as described here, ultimately end in the Supreme Soul. Bodily action means the functions of the senses, and stopping the senses means stopping all bodily actions. But since the mind is active, then, even though the body may be silent and at rest, the mind will act—as it does during dreaming. But, above the mind there is the determination of the intelligence, and above the intelligence is the soul proper. If, therefore, the soul is directly engaged with the Supreme, naturally all other subordinates, namely, the intelligence, mind and the senses, will be automatically engaged. In the Kaṭha Upaniṣad there is a passage in which it is said that the objects of sense gratification are superior to the senses, and mind is superior to the sense objects. If, therefore, the mind is directly engaged in the service of the Lord constantly, then there is no chance of the senses becoming engaged in other ways. This mental attitude has already been explained. If the mind is engaged in the transcendental service of the Lord, there is no chance of its being engaged in the lower propensities. In the Kaṭha Upaniṣad the soul has been described as mahān, the great. Therefore the soul is above all-namely, the sense objects, the senses, the mind and the intelligence. Therefore, directly understanding the constitutional position of the soul is the solution of the whole problem.
With intelligence one has to seek out the constitutional position of the soul and then engage the mind always in Kṛṣṇa consciousness. That solves the whole problem. A neophyte spiritualist is generally advised to keep aloof from the objects of senses. One has to strengthen the mind by use of intelligence. If by intelligence one engages one's mind in Kṛṣṇa consciousness, by complete surrender unto the Supreme Personality of Godhead, then, automatically, the mind becomes stronger, and even though the senses are very strong, like serpents, they will be no more effective than serpents with broken fangs. But even though the soul is the master of intelligence and mind, and the senses also, still, unless it is strengthened by association with Kṛṣṇa in Kṛṣṇa consciousness, there is every chance of falling down due to the agitated mind.
In other words, the uncontrolled senses, agitated mind and misguided intelligence are distracting us from perceiving the true nature of the self. This agitation is due to our false conception of being a purusa (enjoyer) of the material nature, who is disconnected from the Supreme Whole Krsna. Purification of such illusory perception can be done immediately if we engage in the service to the real purusa the Supreme Lord Sri Krsna Himself and this can be done very easily by chanting the maha-mantra:
Hare Kṛṣṇa Hare Kṛṣṇa
Kṛṣṇa Kṛṣṇa Hare Hare,
Hare Rāma Hare Rāma
Rāma Rāma Hare Hare
This is transcendental sound vibration, and this will help us to cleanse the dust on the mirror of our mind. On the mind we have accumulated material dust. Just like on the Second Avenue, due to the constant traffic of motor car, there is always a creation of dusting over everything, similarly, by our manipulation of materialistic activities, there are some material dusts which are accumulated on the mind, and therefore we are unable to see things in true perspective. So this process, this vibration of transcendental sound, Hare Kṛṣṇa Hare Kṛṣṇa Kṛṣṇa Kṛṣṇa Hare Hare, Hare Rāma Hare Rāma Rāma Rāma Hare Hare, will cleanse the dust. And, as soon as the dust is cleared, then, as you can see on the mirror the nice face of yours, similarly we can see our real, I mean to say, constitutional position, "what I am."
Bhagavad-gītā 4.7-9 -- New York, July 22, 1966
Besides the scriptural evidence of the Vedas, there ae other types of evidences. Hypothesis for example is also a type of universally accepted evidence. If you changed your body but remained so many times in this life where’s the logic that you will cease to exist when the old body dies?
Satsvarūpa:They have to agree that the baby's body is gone and the young man's body is gone. They have to agree. But they say that that doesn't mean logically that I have to take another body.
Prabhupāda: What is the other logic? If you have changed your body so many times, why not change this body? What is your reason? Natural course it should be that I have changed so many bodies so this body I shall change. This is natural logic. And what is his logic?
Satsvarūpa: So he said... They say it may be or it may not be.
Prabhupāda: But that is your rascaldom. But this is the real logic.
Morning Walk -- June 8, 1974, Geneva
Ultimately however, the best evidence is to hear the information from the perfect authority of Vedic knowledge. It might sound crazy to a crazy, but this is the only process which can get us from blind faith.
"Since the Vedic knowledge is pure, we accept it. Whatever Krsna says, we accept. This is Krsna Consciousness. That saves much time. If you accept the right authority or the source of knowledge, then you save much time. For example, there are two systems of knowledge in the material world, inductive and deductive. From deductive, you accept that man is mortal. Your father says man is mortal, your sister says man is mortal, everyone says man is mortal—but you do not experiment. You accept it as fact that man is mortal. If you want to research to find out whether man is mortal, you have to study each and every man, and you may come to think that there may be some man who is not dying, but you have not seen him yet. So in this way your researching will never be finished. This process is called in Sanskrit, āroha, the ascending process. If you want to attain knowledge by any personal endeavor, by exercising your imperfect senses, you will never come to the right conclusions. That is not possible."
(Sri Isopanisad introduction)