Truth in Sanskrit is Satya. There are multiple theories on what is truth (ref: http://en.wikipedia.org/wiki/Truth) . However from Bhagavadgita we derive a very simple definition of truth.
Truth is one that is never born nor ever dies. It is eternal; it is constant. Now let us look at some examples to understand this.
Q: What breakfast did you have on 30th of April, 2011?
A: Idli (assuming that the person really ate Idli)
If we ask the person the same question on some other day we expect the same answer. If the answer changes we conclude that the person is lying. He is then telling an untruth. The above answer is now cast as truth for eternity. This question was not valid before breakfast time on 30thApril, 2011 but is valid for all times that and the answer remains a constant.
Next example:
Q: Why do day and nights occur?
A: Since sun shines on earth and earth rotates on its axis
Is the answer true ? Will they occur always? We don't know. As per current observations it is true. There are possibilities that sun might stop shining or earth might stop existing or stop rotating, etc. However once we accept the given conditions, this is a truth.
Q: How does Solar eclipse occur?
Scientific Answer: Moon comes in between earth and sun while it is revolving around earth; it is not deliberate it just happens.
Hindu scriptures: Rahu/Ketu suck the blood of sun for that time and it is an inauspicious time
Which one is true? Many of us accept the scientific answer as true? But why?
Q: Are scientific truths eternal?
Not really. Scientific answers evolve as our understanding of the universe improves. What exactly is scientific way of realizing a truth? What makes us accept scientific truths versus other truths? In short, science puts emphasis on observation and experimental proof. Without experimental proof scientific truths are untrue or mere speculation. These experiments have to be well documented and be repeatable by anyone who is interested to verify the results. It is this approach that convinces us of the validity of scientific truths. One also discovers the path to knowledge is infinitely long and science is the journey with right tools and techniques.
That means as our understanding of the universe improves our beliefs get closer to truths. Our formulas will become more accurate.
Is there anything at all that fits into the definition of truth that we started with? Music, sculpture, other art forms, etc also change over time and hence they don't really fit here. What about mathematics? Maths seems to be different from other branches of knowledge.
2+2 = 4 is a truth!
This truth is eternal. It was never born nor will it ever die. Similarly Pythagoras theorem on right angled triangle on a plane surface is another eternal truth. Thus every truth in mathematics seem to fit our definition very neatly,. Mathematics is a journey by itself to discover truths related to numbers and ascertain if they are really true!
Almost all material objects have birth and deaths and hence they are not truths. Is it fair to conclude that whatever we see in the physical world, the world that we experience through our mind and five senses are not Truths.
This is exactly what is called as Asatya, in Sanskrit. The world as we know is Asatya and Bhagavadgita urges us to discover the Satya hidden behind this world of Asatya. The sun, moon, planets and all the stars appear to be moving around the earth. However we are required to inquire if that is true? The truth is probably hidden and not obvious. The world of Asatya surrounding us is also known as Maya that deludes us of the Truths hidden behind every object and every phenomenon.
Each living being is supposed to be an embodiment of Self, called as Atma. Atma is truth; it never dies, It is never born. It has no emotions, It doesn't change; It is a constant; It is ancient; It is eternal; nothing can destroy It; nothing can burn It, wet It, tear It, etc. It is neither accessible to our mind nor to our sense organs. We can only realize It; there is only Saakshaatkaara of It.
Atma is also supposed to be the same in all living beings. There is no superior or inferior Atma. Atma is no different from Brahman, the God! Thus Atma and God are the ultimate Truths.
Life's aim would then be to realize this Truth; such a realization is expected us to put us in a state of eternal Bliss, Ananda!
Isn't there a similarity between mathematical truths and Atma? In that case what really is Atma? Something to ponder upon......
Coming back to Asatya. The material world that surrounds us is Asatya. They have births and deaths and hence things are transitory. Hence we need to live our life and enjoy the same without getting attached to this transitory world!