There are about 7,000,000,000,000,000,000,000,000,000 atoms in the human body. That's a lot. Our hydrogen atoms are almost as old as the universe, and our other atoms are made of hydrogen atoms. These atoms last are effectively immortal. They are made of energy.
Atoms make molecules and molecules make cells. No cell in the human body is older than 10 years. We are in a constant process of rebirth and renewal for as long as we live. As these cells metabolize, as we live and breath, we swap out molecules with the world. Given the staggering number of atoms in each of us, the math tells us that some of every person who ever lived is in us. When we breathe, we commune physically with all of humanity.
In a very real sense, our loved ones never leave us. The matter and energy that made them is already within us and we carry them forward.
That's to say nothing of genetics. We are all related. Every bit of life on this planet has a common origin. But our families are even more special. Their DNA is very similar to ours, and we carry on the specific arrangement of molecules, the pattern that made them, well, them. We continue the march of their lineage across the ages.
But is that enough? Of course not. Human thoughts can be converted into language. The way we look is delivered to others through the scattering of photons and the reaction of photoreceptors. The unique smell of a person is carried by floating molecules that bind to our own body. All these things created a neurological pattern of that person in your own mind. The memories of how they look, the values they expressed, and the funny little quirks of language are all a part of the living tissue of our brains.
So, while you can not longer interact with the consciousness of one who is gone, do not be deceived. They will always be with you.