What happens to one in afterlife who doesn't believe in God?

Question

What happens to the human in afterlife if he does not believe in any God or any theory related to god?

Do any Vedas mention anything regarding this?

Answer 1

What happens if anyone is not believing in God? What happens to the human in afterlife if he does not believe in any God and any theory related to god?

The answers of these questions are provided in Shreemad Bhagvat Gita by Shree Krishna. Here Shree Krishna is exactly telling Arjuna about this.

अश्रद्दधानाः पुरुषा धर्मस्यास्य परन्तप।
  अप्राप्य मां निवर्तन्ते मृत्युसंसारवर्त्मनि।।9.3।।

aśraddadhānāḥ puruṣā dharmasyāsya paran-tapa aprāpya māṁ nivartante mṛtyu-saṁsāra-vartmani

Meaning - Those who are not faithful in this devotional service cannot attain Me, O conqueror of enemies. Therefore they return to the path of birth and death in this material world. BG 9.3
 
 

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अज्ञश्चाश्रद्दधानश्च संशयात्मा विनश्यति। 
  नायं लोकोऽस्ति न परो न सुखं संशयात्मनः।।4.40।।

ajñaścāśraddadhānaśca saṅśayātmā vinaśyati.  nāyaṅ lōkō.sti na parō na sukhaṅ saṅśayātmanaḥ ৷৷ 4.40 ৷৷

Meaning- One who is ignorant and faithless, and has a doubting mind perishes. Neither this world nor the next nor happiness exists for one who has a doubting mind. BG 4.40
 

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श्रद्धावाँल्लभते ज्ञानं तत्परः संयतेन्द्रियः।
  ज्ञानं लब्ध्वा परां शान्तिमचिरेणाधिगच्छति।।4.39।।

śraddhāvāḻ labhate jñānaṁ tat-paraḥ saṁyatendriyaḥ jñānaṁ labdhvā parāṁ śāntim acireṇādhigacchati

Meaning -A faithful man who is dedicated to transcendental knowledge and who subdues his senses is eligible to achieve such knowledge, and having achieved it he quickly attains the supreme spiritual peace. BG 4.39
  

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तद्बुद्धयस्तदात्मानस्तन्निष्ठास्तत्परायणाः।
  गच्छन्त्यपुनरावृत्तिं ज्ञाननिर्धूतकल्मषाः।।5.17।।

tad-buddhayas tad-ātmānas tan-niṣṭhās tat-parāyaṇāḥ gacchanty apunar-āvṛttiṁ jñāna-nirdhūta-kalmaṣāḥ

Meaning - When one’s intelligence, mind, faith and refuge are all fixed in the Supreme, then one becomes fully cleansed of misgivings through complete knowledge and thus proceeds straight on the path of liberation. BG 5.17

So from this conversation we come to know that people who are non believes or Atheist or who do not believe in God or any theories related ( Shastra) , do not get Supreme knowledge , Eternal peace in this as well as other worlds.They again get rebirth here on earth.So they do  not attain Moksha or liberation, as told in various texts as final goal of Human being.

Answer 2

What happens to the human in afterlife if he does not believe in any God and any theory related to god? Does anything regarding this has mentioned in any Vedas?

Well,not sure about the Srutis(Vedas), but Smritis do talk a lot about the consequences of non-believers of Gods or Shastras(Srutis and Smritis) or the Atheists.

Atheism is condemned all through out Hindu Shastras.Some mention it as minor sin while others mention it as a grave one.

The Manu Smriti mentions it as a minor offence and also says that it leads to loss of caste.

Manu Smriti 4.163. Let him avoid atheism, cavilling at the Vedas, contempt of the gods, hatred, want of modesty, pride, anger, and harshness.

Manu 11.66. Stealing grain, base metals, or cattle, intercourse with women who drink spirituous liquor, slaying women, Sudras, Vaisyas, or Kshatriyas, and atheism, (are all) minor offences, causing loss of caste (Upapataka).

Now,even your question about what one becomes in afterlife as a consequence is answered in Scriptures.

Those who have committed a crime effecting loss of caste, enter the bodies of amphibious animal(Vishnu smriti ,XLIV,6)

So,atheism,contempt of God,reviling the Vedas all leads to loss of caste and loss of caste to rebirth as an amphibian.(HAHA)

In anycase,even if you believe in these "amphibian" things or not, like said in the answer above by SwiftPushkar,non-believers(of Gods and Shastras) will have to take birth after birth.

So,not recommended at all.Have faith and make your life blissful.:)

Answer 3

What happens to the human in afterlife if he does not believe in any God or any theory related to god?

According to the Skanda Purana, Atheists will go to the hell.

Skanda Purana V.iii.227.1-10 “[Sri Markandeya said]…Persons who have no faith, those who are atheists fall into the terrible Naraka. So said Paramesvara.

Skanda Purana V.ii.67.23-31 “…[Isvara said] a voice issued from the firmament as uttered by me in compassion: ‘Do not say anything out of the way. The immutable Srutis should not be censured. The Puranas spoken by Brahma, the creator of the worlds, cannot be otherwise. The atheists who censure the Puranas and Dharmasastras fall into the terrible hell and remain there till all living beings are annihilated.

Skanda Purana VII.I.3.144 “Thus the foolish ones will say, others will laugh. The non-beleivers, the people destined to fall into hell, get their minds overwhelmed by sins. At the advent of Kali Age, they will never gain Siddhi.

Same thing is written in other scriptures.

Mahabharata, Santi Parva 188 “Those that are virtuous in their acts, and possessed of faith, and that have their senses under control, become born as affluent men and repeatedly sport in festivities and heaven and happiness. Unbelievers, with their arms manacled, are sent to regions rendered inaccessible by carnivorous beasts and elephants and full of terrors in consequence of snakes and robbers.

Srimad Bhagvatam 3.9.4 “…we offer obeisance to you (a gracious) Lord who is spurned by the atheists and believers in false logic and who therefore deserve (stay in) Hell.”

Same scriptures also say that unbelievers will be trapped in birth cycle.

Bhagwad Gita 9.3 “Those who are not faithful in this devotional service cannot attain Me, O conqueror of enemies. Therefore they return to the path of birth and death in this material world.”

Srimad Bhagavatam 11.21.1 “The Supreme Personality of Godhead said: Those who give up these methods for achieving Me, which consist of devotional service, analytic philosophy and regulated execution of prescribed duties, and instead, being moved by the material senses, cultivate insignificant sense gratification, certainly undergo the continual cycle of material existence.”

Brahma Purana 65.71-73 “Thus O brahmins is the greatest abode of Visnu endowed with all enjoyable pleasures and attributes. It is conducive to the pleasures of everyone. It is holy and full of mysteries. Atheists and profligates do not go there. Nor do the following go there viz.-the ungrateful and those who are of uncontrollable sense-organs. The devotees of Visnu who worship Vasudeva the preceptor of the universe with devotion, go to the world of Visnu.”

Answer 4

Yes I remember reading a Ramayan Shlok which said it but I don’t have it right now so I’ll add it once I find it

but I only got this Shlok right now which is Manusmriti Adhyay 8 Shlok 309

अनपेक्षितमर्यादं नास्तिकं विप्रलुम्पकम् । 
अरक्षितारमत्तारं नृपं विद्यादधोगतिम् ॥ ३०९ ॥

anapekṣitamaryādaṃ nāstikaṃ vipralumpakam | 
arakṣitāramattāraṃ nṛpaṃ vidyādadhogatim || 309 ||

He who heeds not the bounds of morality, who is a disbeliever, who is extortionate, who does not afford protection, and is grabbing,—such a king one should regard as doomed to perdition.—(309)

And this is the Manubhashya from Medhatithi Ji

‘Disbeliever’—who holds that ‘there is no higher world,—there is nothing in charity—nothing in sacrifices.’

‘Such a king one should regard as doomed to perdition,’—i.e., as going to sink into hell before long.

Source is Wisdom Library

हर हर महादेव जी ਹਰ ਹਰ ਮਹਾਦੇਵ ਜੀ जय जय सनातन धर्म ਜਯ ਜਯ ਸਨਾਤਨ ਧਰ੍ਰਮ